the question is, what is fundamentally necessary about a blowout preventer under the sea, where it cannot easily or readily be accessed? 4 distinct functional realities come to mind:  the rising pipe column must be anchored so that it achieves its own stability via “tower cables” up to a depth of roughly 100 feet from the surface of the ocean.  Therefrom as the pipe or tower is impacted by anything, it will collapse in sections, with the best chance of retaining some control on the bottom.  That pipe needs to be enhanced by, crumple zones/ useful enlargements of a section of pipe that give it a flexible bend if subjected to great stress.   Where the sections are turned or joined together, the simple [a physical spring loaded ramp, that moves out into the stream, with a latch is released, by strain relief or other, these can be reset by submarine; simply pull the stem back out] insertion of “shutoff valves”/ that can be operated by “mechanical, or explosive means, potentially automatic, with fire sensors/ but more secure with strain relief”: at every two hundred feet or so, means you have many options, if the pipe can be structurally retained at the blowout preventer itself, where the last mechanical shutoff is built into the blowout and  established on top of this machine: two of them.  As there is no true possibility of retaining control in the event of a major sinking of a drilling rig, or ship or other: a critical link just above the concrete platform would be “an accordion style section, with structural components surrounding it: break the structure and it folds onto itself in the direction pushed”.  The alternative functional reality is: that the drilling rig must be moved to “the side” once the drilling is done/ OR MORE SIMPLY;   nothing involved with getting the oil is allowed to be directly over the well/ floatation devices or other will support a horizontal section: IF THAT IS REALISTICALLY POSSIBLE. Or a rising pipe that angles at one degree or so off vertical so that the drilling rig is fundamentally distant, and the pipe itself is prepared to bend rather than break.

ALL DRILLING PLATFORMS and other pieces of equipment that are directly involved with oil recovery MUST have fire control systems that GREATLY EXCEED the current level of suppression.  The primary problem after the well exploded, was a complete lack of fire control.  That is IMPOSSIBLE to create with “coast guard spray ships” or any other assumption/ that is not the drilling rig itself.  IN OTHER WORDS:   IT IS ABSOLUTELY NECESSARY, that the drilling platform MUST contain the necessary backup equipment and pumps to use ocean water to quench even the most violent flames.  There must be “sprinkler heads” in place at all times.  There must be high sprinklers on the derrick itself, as well as ANYWHERE, that gas or oil can go.  There must be safety systems in place: such as generating and pumping equipment must be located within the EACH float, COMPLETELY self contained:  so as to have the greatest level of protection from explosions or flame/ with sprinklers from each one in each primary fire location.  There must be a means to “raise the flame”, where the greatest danger of gas escape or oil flames will exist.  There must be “chimneys for raising the flame” wherever oil is stored or piping can burst.  Raising the flame contains it, and keeps it from more critical components, it will drag in stray flames, and give flame suppression a better chance of extinguishing it.   These chimneys can be permanent or applied with hinges or other to fall or move into place when needed. The proof, “the largest oil well in the Kuwait war/ was contained, because they used a chimney to raise the flame”.  There MUST also be permanent slides down to the ocean so that individuals need NOT jump, with fire extinguishers available, or a sprinkler system to clear a path: if they are left behind.  RUBBER RAFTS WITH A PLATFORM FOR LAUNCHING THE RAFTS AT SEA LEVEL , with smaller platforms at rising heights to assure if one sinks/ there is another. ON EACH float. 
If the drilling rig does catch on fire: THERE SHOULD BE, immediate cutoff valving that is automatic or can be manually engaged from various places; taking away the fuel.  If possible an emergency disconnect from the hose and anchorage or other that retains the drilling platform in position must cast off:   so the drilling rig CAN move itself out of this position on its own.  Thereby engaging all propellers to move in one direction, at top speed.  This is to protect the pipe rising.
In addition to that, it is absolutely necessary, that cutout switches be installed to eliminate the possibility of any movement at all, in the drilling assembly: when the pressure testing is being done.  So that NO annular seal, or any other member of the blowout system can be negatively affected.  These can be “closeout boxes” that lower themselves over the controls/ electrical or mechanical switching that must be engaged to operate any of the testing functions, and so on.

The functional relationship of a blowout preventer to the reservoir is: that it represents the “dam gate/ IF IT BREAKS”, THE OIL RESERVOIR EMPTIES, without restraint.  That means: it is absolutely necessary, the blowout preventer does not break.  That means it is functionally necessary to establish weights that are sufficient and tied to the blowout effectively enough to protect it from falling debris, even if a direct hit from a drilling rig were to fall right on it.  That means huge concrete blocks on two sides;   tied together with a platform on top: with access points on two sides to work the controls of the blowout preventer, if necessary. THESE shall contain “slides” so that a submarine can enter these areas, fitted with appropriate matching members and come to rest in the most suitable place for working on the equipment.  The top platform shall contain similar mechanisms, PLUS a secondary hub so that bolting and unbolting by a submarine is possible.  In addition, it would be wise to include suitable slides on the hub to allow for disengagement under extreme conditions, after the bolts are loosened.  That can be done in two different stages, or one by an intricate mechanism of gears which with the turning of one screw by a submarine, all bolts or nuts turn.  With the movement of another screw the slide disengages.  And with a suitable cable lacing and winch the pipe riser can be allowed to rise due to pressures within the flow, while a plate seal (with bolts?) or other is applied to catastrophic failure.  The functioning reality of underwater relies on submarines: the simplest method and most secure method of intervening when trouble comes is, a mechanical screw that the sub can turn.  YOU KNOW how to build a simple slide valve/ and if you incorporate expansion chambers into the shut off/  when this is done: the shock will be limited when closed is necessary.  All blowouts MUST be FULLY tested prior to being used.

It is functionally necessary to be able to change an annular seal, if required.  That means: a new design, MUST incorporate a second annular seal from the very beginning, with completely different mechanisms to operate it.
Other simply methods of shutting off the flow, SHOULD be incorporated as well.  Among these are explosive boxes which the pipe rising, goes through: when activated the explosion crimps the pipe shut.  Strain relief gauges along the pipe determine what is too much.  These should be closer to the top/ so as to replace the damage more easily.  And there should be a shearing box, operated by explosives or other, which once engaged, crimp and shear the pipe, functionally closing the flow immediately with the crimp. And shearing the pipe off, at a predetermined location so as NOT to take down the entire riser. At least two such shears should be in place, which will operate based upon a different set of strain gauges that determine whether or not the tower cables are coming down or other, as would indicate collapse.
As a final means of defense the introduction of a very large upside down funnel, which can be later hooked up relatively easy with a flow pipe from above for siphoning or pumping oil, in case of a massive leak.  Methane is not a problem IF YOU PUT the funnel high enough.  Oil and gas rise on their own/ and will continue in the path they select.  That means it is only necessary to eliminate the freezing caused by gas escape.  That is VERY simple to do, by simply letting the water provide the heat/ even at 32 degrees, there is enough heat in the water to remove any trouble this causes.  Once a flow is established, if you have the right equipment in place, it can and will collect everything.

EVERY employee that works on this equipment SHALL BE TAUGHT, every aspect of the work, so that THEY KNOW, what is safe, what is dangerous, what they can do in the event of an emergency to stop the processes causing trouble.  THEY NEED TO KNOW, and you shall teach them to watch over you, the rig, the environment, and their own lives.  They are then responsible, and once every month they will individually report by public internet (NO hiding) on the process of the work and all aspects of the equipment or drilling.  They will include aspects of what they have been taught or believe, so that anyone who knows can become aware of this is or is not correct. Every six months or less: paid inspectors SHALL investigate these interviews of the men and their bosses, and every person involved in the decision making: ALONG WITH THEIR DIRECT INSTRUCTIONS to the platform.  NO decision is made, UNLESS it goes to public forum first/ let the people have their say.  All decisions below the surface of water SHALL be the safest method possible, without exception.  Failure to abide is a criminal felony offense, and those who give the order shall go to prison, for not less than one year: hard time.  Those who obey that order having “should have known better” WILL go to prison for at least 6 months.  If anything goes bad in the future: because “you were gambling, with our lives, environment etc”/  death is not unacceptable. IT IS a serious decision/ don’t do it!  DON’T gamble with our lives, our environment, or our future.  Undersea video cameras should be placed and working, as the public and inspectors desire.  Not less than once a year: an entire video shall be made of the entire working site and equipment.  Once every six months when drilling of every single well.   This can be done by lowering a camera on a cable down the well riser pipe.  This will be done by independent submarine owners who will be paid for their inspections, once a year per well: cost to taxpayer.

THESE ARE necessary changes to the work.  They are then completely within the costs confined by public safety to the person who buys the fuel.  YOU PAY FOR SAFETY/ because you want the fuel, and the environment, and money MUST NOT INTERFERE!

This spill arises from a failure of the entire american society, and those companies involved.  YOU are so damn greedy safety is not first/ SO DAMN arrogant, “gambling is what your leaders, business, and university do”/ SO DAMN corrupt, nothing matters but your gasoline, gluttony, and comfort.  And so damn stupid, you are prepared for nothing/ knew it, and still did nothing. To your shame as a nation, this occurs. Just so its clear, BP is NOT responsible for a debts created by your own moratorium: the oil industry is/ and they share an equal burden of guilt and shame for this leak.  They are not prepared/ they gamble everyday/ it could easily have been their fault.  It is the US government employee and bureaucracy  fault, for absolute failure on all counts.  “Just stealing the money, for themselves”.

This well represents the gluttony and thirst for oil and money, that is so prevalent in this USA. The tragedy has already cost an environment, that may or may not be recoverable/ loss of incalculable sea life, it threatens much more.  It has invaded your own food supplies, threatens by hurricane to dissolve even more.  Disturbed or destroyed business, industries, and home life for millions.  And yet very many people want to continue “exactly as they are”; because greed has no holiday, and consumption does not know when to stop.  You are still eating, be happy.  You still have a possibility of cleanup before it becomes an ending of this way of life; work hard, do what you can.  This is not, “simply BP’s fault: although they are certainly going to share the blame and cost”.  Rather the cause,  is an american way of life: greed, greed, greed; give us more oil/ we don’t care how.  Find some sanity!  Grow up.
The “university built” politician is: “pretty words/ little substance/ big dreams/ & nobody pays really, fantasies are wonderful”.  Is that not exactly where you are today?  All the trillions given away are not creating jobs, because the money (entirely inflation, because it cannot be paid) is being used to steal your homes and destroy your business.  Someone, is getting the money: is it you!  Just the increased debt for this year, $1.6 trillion dollars represents 100 million people taking out a loan of $306.84 each and every single week.  Did you know as one of those 100,000,000 people, you were taking out a loan of three hundred and six dollars each and every week?  SOMEONE IS getting this amount of money/ and they are handing you the bill.  SOMEONE IS, spending this amount of money: and you can bet, they are buying foreclosed properties, so they can make you slaves, “going to be rich”.  Think for a second.  Think about all the other threats, and learn to do better: read this site, as a beginning. OR YOU WILL REGRET IT, because there are no second chances, it will be war, on everything and everyone.  The price of lies, theft, cheating, pride, want, selfishness, hate, and so on.  But with a “thousand threats than can make you extinct: what the hell, right”?  Answer the question.