Sounds like you have theft proof stands. Id be more interested in learning about those than keeping people out. Only stands I have had stolen off public land were at locations I knew better than to leave them. My suggestion would be to lose your trail markers(bright eyes tacks, tape, etc) and get away from obvious stand sites(near trails, parking areas, field edges, etc). If its easy for you to acces/find, it's probably easy for thiefs too. Carry a climber to those places.