simple solution to hijacking problem

It's very easy to "arm chair qb" on Monday morning! Could've, should've, would've.....it's easy to say how tough we are and what we would've done, but the fact is none of us know exactly how any of those people on those flights felt, one could only imagine scared out of their minds, wondering if they'd live another day to see/speak to their family and friends again. It's a given: airport security must be improved, air marshalls on all flights should be a standard, and impentrable cockpit doors should be installed on all planes. If the terrorists knew they couldn't get into th cockpits, there'd be no sense in killing stewardess' or other passengers, cause they'd just have armed soldiers waiting for them on the ground when they landed. Granted that would only stop hijackings, but it'd be a step in the right direction.