I used to work at a bike shop, so i have a bunch of combination chain and cable locks. I also use the flexible gun locks for the trimmer rack. But i was debating about purchasing one of these to prevent the walk offs while I'm away from my truck and trailer. http://www.etrailer.com/c-toylok.htm
It doesn't matter what type of lock or chain you use, if they want it bad enough they are going to take it. Locks and chains just prevent joe dip **** from walking through the lot and taking it.