Problems with Groundhogs

I am not sure if you will be able to help me with this but I don't know what else to do. I live in the Holland Marsh (Bradford, Ontairo, Canada) area.
In the front of the house and along the side of the porch I have a full shade garden. At this point I have in the garden a boxwood, some 3 hostas, and some alyssum. In the very back of the garden I have just this year planted some ferns. Three years ago a groundhog decided to try to dig in and under the porch but on the other side of the porch from the garden. We were able to put down cement stones and stopped him from digging on that side but for the last 2 years he has been digging in the garden. He usually digs in the back corner but on the porch side. We keep filling it back in and he keeps coming back and digging again. We have no idea how to put an end to this. The fern that I planted there is gone but so far the hostas are surviving. Is there anything that we could plant to discourage this animal? If there is not then do you have any ideas on what we could do?

There are several ways I have heard of that might help.
There is a sound device that can be used to chase away ground dwelling rodents. It is called "Sonic Gopher and Molechaser". I bought mine from Lee Valley in the Toronto, ON, Canada area. The USA company that makes it has a technical support e-mail address : techsupport@p3international.com
There are plants available whose roots to rodents taste or smell so dreadful that they will go elsewhere. I don't know how far away it drives them. The plant I recall seeing advertised some years ago was in the milkweed family. Mint is supposed to repel rodents too, but since it is very invasive, the other remedies might be more appealing.
A live trap can be borrowed from the Humaine Society. Bait it with fresh vegetables and release your catch many miles from your home near some conservation area. Source: nic@niagara.com
If you are more bloodthirsty, smoke bombs are available from co-ops in agricultural areas. The holes of the gopher are closed with tightly packed earth, the bomb is lit, stuffed into a remaining open hole and then this hole is also tightly closed. If all holes were closed the animal will die in the burrow, before it can dig back out.