Folks...I'm curious about this... with regard to the Gulf Oil Leak... I'm wondering if there is existing technology such as the following:
(if not..consider this my informal patent application haha)

All wells in deep sea, should have an 'auto-shutoff' stop valve at the bottom..where they enter the seabed, such that if anything goes wrong up top... it automatically shuts off the flow.

It wouldnt be hard to rig this up I'm sure. something like what we in electronics call a 'watchdog' timer.. unless it is refreshed every millisecond or so..it causes a RESET and a restart.

Do they exist ? Do they cost the earth plus plus? Are any wells using such ?

Any problems with using this approach?

Yes Al there is such a device.
It is called a Blow Out Preventor.
There is one on the BP well and it is four stories high, so they say.
However it failed !
Hmmm

In a perfect world, one wouldnt have an oil rig in the first place without having a contingency plan for when things go wrong...
But you could say the exact same thing about a lot of industries, such as nuclear materials, paper manufacture, mining sulphidic ore bodies, the timber industry, the concrete industry, the native plant and animal industry, agriculture, etc. etc.

It makes a lot more sense and is much cheaper to rename the problem, which is why I reckon they should urgently rename it "The Sustainable Murray River".