I was surprised to read this follow-up post where you mention your dog, because that is what has kept groundhogs away from us. I dimly remember my mom dealing with them in her garden here when I was very young (pre-1970), but none since then. Then sometime after my mom died and her last dog passed away a pair moved in and grew to be a clan.
When my husband and I moved back and he got a dog (lab cross), that dog dug every groundhog hole entrance into a massive crater. He never hurt them, but they clearly no longer liked the neighborhood and I have not seen hide nor hair of a hair of a groundhog since.