According to Bruce, none of the predominantly used mechanisms (ID cards, face recognition software, screening attendees) work. The one solution that works is:
"...smart security officials watching the crowds. It's called 'behavior recognition,' and it requires trained personnel looking for suspicious behavior..."
But even then, there is no way to stop a really determined terrorist willing to die in the process of committing the act. If he is not able to blow himself up at the location of his choice (bang [pun unintended] in the middle of the spectators in a stadium, for example), he would then do so at the checkpoint where he is about to be busted.
I have a simpler solution: as Michael Rivero is often wont to say, stop messing with other countries' people, and the terrorists will go home. But then what do you do with the home-grown variety? Try to ensure that there are no alienated groups ready to take to violence because they feel that justice is being denied to them. This may not solve the problem completely; there will always be someone with a grievance (real or imagined) that is not being addressed, but application of the 80:20 rule (80% of the violence is due to 20% of the causes) will at least make the problem manageable.
