Terrorists in kayaks may sound silly, but the boats are very quiet and low-profile and can zip along in just a few inches of water. Granted, they wouldn't be going very fast if they had 600 pounds of something in them, and they'd certainly need enough water under them to hold them up. Here in Florida, I'd watch for them around shipping along the coast or the St. John's - and near nuclear power plants, which are, of course, located on rivers that are filled with perfectly innocent recreational kayakers. What better cover?
There would be no problem putting motor mounts on kayaks either.
Knowing what I can do with my rigs makes this article pretty spooky.