Do a google seach for hitch lock. You will have many options. Also check out trailer tire boot.
We had a neighbor selling a 4wheeler. The ATV was loaded on a trailer with a boot installed. One morning on my way to work the trailer and ATV was about 100 feet down the road and on the other side of the road. I guess someone tried to steal the whole thing but couldn't tow it, so they disconnected and took off.