I would shoot them with an powerfull airsoft or paintball gun.If that dosent teach them try for a light pellet gun.one problem you need to watch for is make sure they dont become comfortable on your property and become feral.Its happened to me before with a lost beagle.tryed everything for2 years.I hated i but finaly i had to kill it.If you do have to kill it make it quick,and dispose of the bodys.