My 2 cents...
I figured all the locks and chains I might add wont stop anyone dedicated to taking my 6x12. I also figure if it is going to happen, it would probably be at night.
Oh, I lock things as best I can, but hey, they have battery operated 4" grinders these days. So, I added one additional electrical trick to make the thieves night a little bit more interesting.
I'd imagine, he/she has their lights out as they backs up to capture in any fashion. They connect the lights at some point, be it right there or down the block, I don't care. When they do, they immediately blow the taillight fuse on their Tow vehicle, leaving them with just headlights and brake lights. And, when they step on the brake, they blows those out on the tow vehicle too !
I doubt they are prepared they are prepared for that. They will either dump it or run, and if they run, odds are SOMEONE will see them with no lights.
It is very easy to put a single switch (DPST) in that will electrically short your brake and tail lights to ground. Flip it on when parked. Just remember to turn it off when you have to tow it !
It really does not take much to realize you can set up a timer circuit that detects the blown fuse and sets all sorts of light and sound into motion if you have battery power in the trailer. Police get real curious when people other than them are running down a road with blue and red flashing lights for example.