Much as I enjoy entertaining visitors on my flight deck, the only way to defeat this problem is 1)inpenetrable flight deck doors (I believe El Al already has these), 2) a video camera in the cabin with a monitor in the flight deck, and 3) on-board security (again, I believe El Al already do this).
Crews need to be trained to be assertive here... if a terrorist is cutting Cabin Crew throats, when you open the door you can virtually guarantee that you and all the pax will be dead in short order... NEVER open the door. Depressurise the aircraft, do some aerobatics, whatever... but don't open the door. Just land ASAP. Once terrorists know that they will be physically unable to gain control of the aircraft, the problem recedes.
As many, many experts have said over the last few days, it is impossible to defeat the determined terrorist by prevention alone. Sorry Danny, but on this one you are well wide of the mark.