A couple of years ago, she chased one up in a tree. Groundhogs make a funny clicking noise when threatened, and have some pretty wicked claws and teeth. But they are very shy and not dangerous unless they are cornered (which, as I mentioned, my dog likes to do.)
When we can, we use a rake to push the cornered creature into a trashcan, and then we enter him in our "relocation" program (which means we drive him to a field down the street and release him, then he is someone else's problem). This sport is referred to as Groundhog Wranglin'. What? You've never heard of it? Well, that there's the way we do it here in the deep South of Jersey.