For groundhogs, pour fresh urine - yours or a horse's straight down their holes. Then, pack with fresh horseshit. It will abandon the hole. This worked for me. For permanent treatment, get a hounddog. Mine eats them. Another option is to get a ferret, muzzle it, then drop it into the GH hole. It will kill the GH. If you don't muzzle it, it will simply kill then eat, and won't have any desire to kill more. If you have only one - fat chance! - then forget the muzzle. R.