I would say, IF he had permission (and I would check it out), nothing you can do to keep him off of property. BUT! If they were YOUR stand(s), he had no right to use them and should have been asked to move.

I personally wouldn't want to hunt close enough to smell another hunter. Too close! Kind of like walking up right next to a guy shore fishing a huge lake.Give them some room!

Ethics would depend on his right to be there in the first place.