I'll post again on the subject because I believe this is the best tree stand lock ever invented and it's worth every penny of the $20.00 it cost.

http://www.sportsmansguide.com/cb/cb.asp?a=145438

The lock attaches to the tree via an eyebolt you screw into the tree about 2". The lock then covers the eyebolt leaving nothing to be cut. The way they show it set up in the pic is upside down from how I lock it. I like to lock it with the key hole pointed down for two reasons. the first is obviously to keep water and grime out. Second if someone were inclined to try and smash the lock the wouldn't be able to get a good swing at it.

I've really looked it over and I think it's fail proof. Only time will tell.
*one last note. I pickled up a few of these at wallyworld after the season ended last year. $10.00