In article -
september.org, says...
Darrell Ulm said:

Hello. We have a ground hog family living near the garden. They like
to eat everything. will a few moth balls down the hole do the trick or
are they too toxic?

Trapping and careful fencing are the only non-toxic, non-fatal solutions
that I can vouch for.

As for killing groundhogs, shooting is very effective when done by
someone skilled.

If you can run them into one of their midday bolthole / bivouac
burrows, gassing works pretty well (use 2-3 Giant Destroyer smoke
bombs taped to the end of a bamboo pole and fill in the entrance).
This is less effective on a full burrow complex, because they have
several entrances, including some that are hidden (no fan of fresh
dirt).

Some useful informations and products for sale he

http://www.bugspray.com/articles99/woodchucks.html

(I have ordered from them in the past. Not much for web design,
but very informative.)

Using fencing with trapping is better.

They either tolerate mothballs or push them out of the burrow.

What people don't realize before they lose a crop is that these "cute"
eating machines are ****eating machines****.

When you go to transport them, put plastic down and several thicknesses
of newspaper over it. They normally leave a parting statement.

When they are gone you are left with cleanup apart from the trap. That
is, you have to fill _all_ the holes. Skunks will use burrows. Transient
groundhogs will take up residence. If you can get the neighbours to fill
in every hole they find, you'll be several steps ahead of the next
assault. ...There's at least one male nearby.

My experience suggests that filling with something undiggable is better
than just using soil. Passing groundhogs will redig old holes. I fill
with saplings or whatever depending on location and what I have. Usually
to a foot or two below the surface if we need to use the area.

In one area I put down a subsurface layer of chicken wire... It'll be a
PITA at some future date, but it's prevented digging in a difficult to
police area for several years. (There was no other option or material at
the time.)