Removable steps will help deter thiefs, but they're not gonna work 100% of the time. You'll find a lot of lowlifes carrying screw-in steps around with them just for the sole purpose of stealing treestands.
Chaining/cabling/locking a stand to the tree will also deter thiefs, but once again not all the time. Too many people with hacksaws and bolt cutters out there these days.
The only way I've ever found to stop thiefs is simply to take the stand with you when you leave. Hunting out of a ladder type stand isn't very much fun when you have to take it up and down all the time, so why don't you try using a climber or hang-on? I use Loc-On and Gorilla stands and they're very easy to get in and out of a tree. Usually if I'm leaving it only overnight and coming back in the morning I'll leave it up, but if I'm gonna be gone for a few days I take it down. The thing is, you usually don't have to take it all the way out of the woods with you. A lot of times I'll bury my stand under a deadfall and cover it up well enough that it can't be seen even when I know where it's at. Thiefs are never gonna find it then.
Last but not least you can sit out in the woods 24 hours a day and when the SOB comes by to steal your stand you can shoot him in the back and bury him in a swamp where nobody will ever find him.
