I wouldn't call myself an expert on groundhogs, but I've hunted them most of my life, studied them, and interviewed shooters who are real experts.
I'm a long way from knowing everything about these little varmints, but I've learned a few things and one is that they're smart and wary, and once an idea settles in their little pea brains, they can't be discouraged. Not by anything at all.
For example, they love my garage and generation after generation has burrowed inside and around it, so much that I finally had to have the floor paved with six inches of cement. Even then they persist in digging holes around the outside. I've tried moth balls in their holes (doesn't work), other repellents, live traps baited with apples and carrots, and eventually found the only thing that does work, at least if you live in the country. Which is a 12-gauge shotgun loaded with No. 4 magnum turkey loads. I'm sure that anyone living outside town with a barn, garage, or other buildings will understand.
Still;, the little chucks do have their good points, though they're few indeed. One is that they make for great PR with landowners. I once said in these pages that a single groundhog can eat $50 worth of soybeans in a year, but that's not true today. With bean prices sky high these days, that number is closer to $100, which can put a real dent in a farmers wallet if he's got a couple of dozen loafing in his fencerows.