ORIGINAL: c_str
Now I don't think they can use your tree stand, but they can certainly stand right next to your stand, if they get there first.
Sorry man but that is what public land is. Maybe your state has different rules/laws regarding stand usage etc.
Actually, in Michigan, if you leave your treestand on state land, it is legal for someone else to use it - as long as you're not in it. This is according to the 2008 Hunting Trapping Guide:"If you hunt on public land, your tree stand must be portable and your name and address must be affixed in legible English that can be easily read from the ground. Your name on a tree stand or ground blind on public land does not guarantee exclusive use."
I wouldn't do it, but that's the law!