The best way to get woodchucks/groundhogs to quit using a particular burrow entrance is to put used cat litter at the entrance/around the hole/down in it. They create pretty elaborate networks between openings to the outside, so they'll just shut down that tunnel after a while and you can fill it in after they stop using it.

Groundhogs are vicious, though. They're the only animal my jack russel has some trouble killing on our farm, so he only goes after the little ones now.