I've been battling groundhogs every year to some degree. They are wily and tenacious little suckers. Wish I could tell you I've discovered a 100% surefire solution, but that just wouldn't be true.
I could never convince mine to venture into the Hav-a-Heart... even when baited with potato chips and apples (an allegedly "irresistible" combo.) I tried Hope Hoops hot sprinkle method and tossed garlic and onions around their nest hole. I even had mr beac pee in a bottle and sprinkled that around the perimeter. Nothing really kept them completely at bay.
I think I may have accidentally hit on the best method so far just a few days ago. I've seen this year's pest a few times popping in and out of his chosen place, fortunately NOT under our house like last year's (we did extensive nest-prevention around the foundation at the end of last season. One thing to know is that they build those things with more than one entrance/exit, so if you want to block them out or in, look around that tree for the other "doors."
Well, the other day another member of the house saw the groundhog too. Our dog. He (the dog) busted straight thru the porch screen and attacked that little garden thief.
We only realized this had happened when we heard squealing. Mr beac yelled "DROP IT!" before we realized what it was (we were terrified it was one of the neighbor's chickens) so he didn't manage to kill it, but with a bite pressure in the 1200lb range, I'm sure doggie's fangs put a severe hurting on the pest. We've not seen or heard a peep from it since.
Do you have a dog? Maybe take him outside for a garden stroll every evening? 5-7pm seems to be the time they are most active around here.
One other thing to try if you get really desperate is "feeding" them. Last year, I'd put the peelings, chop ends, cores, etc. of the veggie and fruits we were eating next to their other nest (not the one under the house) and that dramatically reduced the raids on the actual garden. We live in the country, so not sure how this would go down in the suburbs.