Take the stand out and use a climber.

I agree with Jim

Rig the stand to where it can't be used except by you and your brother, ametal stripstudded with nailschained to the seat comes to mind. Anyone with a welding machine can fab it for you, and if only you two have the key the neighbor is SOL.

just put screw in steps up the tree and take them out when you leave.

Take the ladder away when you are not using the stand.

I feel you buddy, this past season on private property that the owner has given only three people permission to hunt being myself and two friends. Someone hunted out of my blind, left the windows open and stole my seat. They also stole the seat from my permanent stand about 50 yds from where my blind is. Then they had the nerve to write in the snow " We got your deer and F you"

IMO, If you start the booby trapping game, you have opened a can of worms that may never end. You will be trading traps and someone is bound to get hurt. Lawsuit!

If this were my problem, I would talk to the guy. There is not reason not to unless your are scared of confrontation. Also, explain the situation to your father. I know you have, but be convincing. He should back you instead of this good for very little neighbor. F'him and tell him to stay off your land and out of your stand!

Post a picture of the treestand.
And we can come up with an idea.

I'd walk over and speak with the guy, quite a concept isn't?

I'd snap... wouldn't be a pretty sight..
Had that happen last year... guy (drug addict) climbed into my stand, shot a buck w/ the bow, and left an empty beer can at the bottom of my tree!