IMHO, 24-hr surveillance of heavily-trafficked areas would be more effective. Then send one dummy Humvee into Fallujah by radio control, blow it up, and then detonate a secondary explosion 15 min later (to get all the cowardly body snatchers and dancers). I like that kind of thinking.
That destroys the vehicle, though. Wasteful. But a release of a suitable chemical agent would offer no such difficulty....