I once saw a show on one of the cable channels about some monster hunters on the tail of the giant octopus. It was pretty dull, since I can't remember anything about it save one point: they mentioned that a giant octopus was rumored to live under that particular bridge, but they weren't allowed to dive around the bridge for security reasons. That struck me as being pretty silly, because that would seem the best way to ensure that a saboteur would be able to work in peace and quiet. If the police can't get around to their growing piles of arrest warrants, then they surely can't find the time for regular inspection diving. Best way to find those discus shaped thingies with the red blinking lights is to encourage civilians to get out more.
Think the same applies to airline travel. The chances of an airliner getting hijacked are pretty low right now, and it has nothing to do with the valiant efforts of the noble TSA. Citizens are your best defense here, and it costs nothing.
I assume the biggest problem is that of explosives, and I have to confess to some confusion: What's with all the x-ray machines and groping in the name of safety? Why not subject every traveler to a good sniffing by a bomb animal? They appear to be accurate, cost very little, and I'll bet people would rather have a giant rat crawling through their clothes than a sweaty human.