Most likely if a thief makes it up to your stand, he's going to take it. If you use a chain-on you can get a tree stand padlock (they even make them in camo!) . But if you can make reaching the stand difficult they'll be less likely to make the effort.

When setting up your stand, keeping camoflauge in mind for the stand is a good idea not only for deer but also for thieves. There's something about a stand sticking out like a sore thumb that I think calls to thieves.

I like to use climbing sticks. In some areas I'll pack the sticks in, but other areas I hunt that's just not feasible in the dark, so I'll find an out of the way spot nearby (but not too nearby) and bury the climbing stick under leaves and sticks. I have a climbing harness style safety harness which makes it easier to put the stick back up quickly and when I reach the top I just get right into the stand.