I deal with similar issues from people who get permission to hunt a farm to my south. I usually place a NO HUNTING sign right in front of their stand. The last two years they have actually cleared shooting lanes onto our property so I fill those back in, placed a scarecrow on our side of the property line by their standand last year I cut out the regulation about shooting deer on property that you do not have permission to hunt on and placed it on their stand seat. Their stand was gone the next day.