I have used a paintball gun on my old neighbor's dog and it works! This dog was coming from 2 houses down onto our 5 acre property which was next to a family member's 33 acre property so fencing is not always cheap or effective whe you're dealing with a large piece of land; t-posts, line, and an energizer are expensive for those of us on a fixed buget. We only had rabbits and dogs at that time but our dogs are american pitbull terriers. They were chained in kennels but this dog would come onto our property and go to our dog's gates and harass them to the point that one gate was completely destroyed from the inside several times because my dog wanted out so bad. I took every precaution to prevent my dogs getting loose but this neighbor didn't care. We talked over and over warning him that we exercise our dogs in the field off-leash and if something happened it wasn't our fault. It didn't matter, the dog was still allowed to roam. The last straw was when the dog was trying to get our rabbits from the bottom mesh of the cage. We didn't want to kill the dog because it wasn't the dog's fault, it was the owner's. After a few incidents with the paintball gun, the dog never came back; it scared the dog away every time. I'm not positive contact was ever made or if the owner decided to contain his dog or not but it didn't come back.