Signs that you have a groundhog problem include:
Large holes in your yard from 10" to 12" wide, next to mounds of dirt
Disappearance of plants and vegetables in your garden
Damage to structures like fences or sheds
A foundation that appears to be sinking near the holes in your yard
To determine if groundhogs are still occupying a hole, place a few sticks at the entrance and check within a day or two to see if the sticks have moved.