Scum. I must admit I've had many a sleepless night worrying about somebody nicking a boat, or at least something off it. Depending on where it's left of course. I use two wheel locks, an alarm cable lock that flashes red in the night, plus I've got a lock base fixed down into the concrete, with a high security chain locked to the trailer. The boat is on my back drive and isn't really visible unless somebody peered over the back gate, which is also locked. I would say it was almost impossible for somebody to nick it, bearing in mind I've also got a dog, and somebody would have to make the most horrendous noise in the middle of the night to try and nick it. The only hope somebody would have is picking the locks, as cutting them would be out of the question.
Don't be afraid to Think outside of the box.