just put a taser on the seat....I know a guy in Taiwan that manufactures and sells a front-wheel locking device for scooters. In Taiwan scooters are everywhere, it's insane how many there are. The great thing about this device is that it alerts you that your scooter is moving, where and at what speed. When the thief gets up to speed, you can push a button and it locks the front wheel instantly! Good times ensue.
I suppose if you made something like that for your trailer, maybe locking up only one side for maximum fun, you'd get sued or go to jail for harming the thief. Remote actuated explosive bolts for the trailer axles could be a lot of fun also.