A 12 ga. shotgun works real well...but likely not probable in your community garden.

I don't know of any inexpensive OR expensive way to deter those things. If they want to go someplace, they're gonna get there, one way or the other.

If you's decide to bury wire fencing...make sure it's a strong wire. Hog panels would be wonderful, but...they aren't cheap.

I even tried live trapping them & using one of their favorite foods as bait...an apple. No such luck! I'd watch 'em look into the trap & mosey right on by. They are one smart critter.

Good luck.

Connibear traps. They'll dig under 2 feet of concrete, so buying fence or concrete won't stop them. They'll also climb over most any fencing. Connibear traps. Or if you're going to use Hav-a-hart traps and relocate them, they like apples and they love cantaloupes. Their favorite garden vegetable seems to be sweet potato leaves, and it's impossible to grow sweet potatoes with groundhogs around. They also like cabbage. Years ago they ate the hearts out of about a dozen cabbages in my garden--and that's when I learned that a cabbage with its heart eaten out will sprout 4 or 5 smaller cabbages to the side of the main cabbage that's been eaten. Also, spread some peanut butter in the trap for the odor.

Ok I have a house in the country. We have a raccoon that now lives in our crawl space under the house. We have seen it on the security camera more than once. It must have been trapped at one point because it is now trap smart. HE knows how to reach in and get the food out and not get trapped.
So if you do trap the groundhog please do not take him to the country and cause issues for the farmers. Trust me as soon as a farmer can he will shoot it. I grew up learning how to shoot and our targets were groundhogs in the field.
The only way to rid your garden of a groundhog is to kill it. They can climb over any fencing, or dig under. They live in dens, so they can dig to China.
Sandy

We are experimenting with baiting our Havahart trap with pea sprouts, which of course are always one of the first things the groundhog dines upon in the garden. We just planted some in a planter are are putting them in the cage.

Ali in Maine

I have been using a small, battery powered, electric wire around my garden successfully for 4 years. The shock is pretty mild and won't kill anything - but if you touch it you will say 'ouch' outloud.

You put up your regular fence and run the electric wire on plastic posts all the way around, just outside the fence. I have it doubling back and forth so it's one long wire at 1' high, 4' high, and 10' high.

We had a family of groundhogs under the back deck two summers ago. They stayed out of the garden until one day when I saw the whole family in there eating the lettuce and peas. After chasing them out I discovered that the batteries had gone dead in the charger. I replaced the batteries and no more problems. It even works against deer. Turns out the deer will try to push under a fence first. As soon as they try that they get a shock to their nose and take off. We are in the woods with a large deer population and we have no deer in our garden!

The charger I use is the Fi-Shock SS-2D, catalog # CH-02 at http://www.mrmcgregorfence.com/products/parts/energizers.htm

It runs on 2D batteries for about 3 months. You can get just the charger and buy posts and wire locally, or you can get a whole kit from Mr. McGregor's Fence.

I highly recommend this, it's the only way I can garden in the woods.

Here is a link that might be useful: Electric Garden fence

The problem with conibear traps is that they will also kill anything else that goes through the opening, like cats and yappy little dogs, so they are best used in the groundhog's burrow entrance, not the garden fence.

We quit baiting our Havahart live trap and just let it sit open along side the garden fence. Everything is curious and gets in it, especially young of the year animals out exploring. Groundhogs, raccoons, oppossums, and skunks are the usual catches. A trap that has recently caught an animal seems to be more attractive to others, and catching a skunk is the best to draw other animals in, even if it doesn't spray. The only problem is that skunks are kinda dumb and I catch the same individials over and over again. Skunks don't bother the garden so I simply prop the trap door open and let them wander out of the trap on their own.

I have even caught groundhogs in traps bloody from the last raccoon.