The best way to prevent further incidents like this would be to remove the bloody door altogether and replace it with a locked but breakable door, if someone attacks the door leave it to the crew and pax to defend it, if need be though it can be broken down.
Thank you Ollie Onion.
Leave it to the crew and pax to defend it! Exactly! That is what the security goons and clueless pollies do not understand about a post-911 world.
If ANYBODY now tries to make an unauthorised flight deck entry, thanks to 911, they will be torn to pieces or at least have thier ribs broken by the pax and crew.
There is your defence of the flight deck! Do not make the flight deck impenetrable, it might cause an accident.