According to collegeboredom.com, there are eight ways to kill a groundhog:
8 - High precision sniper rifle.
7 - Feed piquant mustard to his shadow.
6 - 2 cups soy sauce, 1 tablespoon of sugar, and a grenade.
5 - Make him try to solve a Rubiks Cube. (I've done this, the groundhog explodes)
4 - Make a bet with him that he can't drink two gallons of milk in five minutes. (groundhogs are suckers for wagering)
3 - 1994 White Ford Bronco. (self explanatory)
2 - Make him watch Groundhog Day starring Bill Murray over and over again. (again, he explodes)
1 - Hire this guy.