This past March I attended the Nashville Lawn and Garden show at the State Fairgrounds. I was walking around and I saw a video similar to what Blue posted with the Rodenator. This fellow was called Pappy's Mole Service. He had the wand that used propane, he filled the mole paths with propane and ignited it. The moles went BOOM! I so much wanted to buy one of these things but he was not selling them, he was selling the service. It was a hoot. I was talking with him and his wife and I suggested to them that they should get a booth at the gun show. Guys like to blow stuff up and watch stuff get blown up, they might be able to sell their service at a gun show. I told Pappy that moles were eating my sweet potatoes, he said that the voles go into the mole tunnels and they were nibbling on my sweet potatoes. This season I criss crossed chicken wire in an old compost pile, added a 10 inches of soil. I hope that keeps out the moles/voles.
As far as groundhogs I have blocked off all of their holes in a 30 foot long mound except for one. I have a chair set up about 40 feet from that hole. If I see any damage in the garden I make sure the holes are still blocked, sit in my chair with the 20 gauge and vanquish the groundhog when he presents a good target. Groundhogs are evil beings, they can climb a three foot fence and get into my beds. Last season they ate my broccoli, and three different types of lettuce. They are not fond of spinach.