Are you sure it is groundhogs? Sounds like a badger to me.

If it is a badger, they are after ground squirrels. You should see "grass" piles where the badger got to the "squirrel" nest. 

When we get an occasional badger, they tend to go down the road digging up ground squirrels for miles in a straight line.

If it is ground hogs, get a badger!