The NYT asked Bruce Schneier what to do about terrorist attacks like the failed Times Square car-bomb. I really like his response (unsurprisingly!).
Think about the security measures commonly proposed. Cameras won't help. They don't prevent terrorist attacks, and their forensic value after the fact is minimal. In the Times Square case, surely there's enough other evidence — the car's identification number, the auto body shop the stolen license plates came from, the name of the fertilizer store — to identify the guy. We will almost certainly not need the camera footage. The images released so far, like the images in so many other terrorist attacks, may make for exciting television, but their value to law enforcement officers is limited.
Check points won't help, either. You can't check everybody and everything. There are too many people to check, and too many train stations, buses, theaters, department stores and other places where people congregate. Patrolling guards, bomb-sniffing dogs, chemical and biological weapons detectors: they all suffer from similar problems. In general, focusing on specific tactics or defending specific targets doesn't make sense. They're inflexible; possibly effective if you guess the plot correctly, but completely ineffective if you don't. At best, the countermeasures just force the terrorists to make minor changes in their tactic and target.
