How can we keep groundhogs from eating...

In addition to installing an electric fence, there are several solutions. Try feeding them Juicy Fruit gum. Buy several packs and unwrap each stick. Place the sticks in the garden where the groundhogs have been eating. They will eat the gum and go away. Or try sprinkling blood meal or talcum powder around the perimeter of the garden, or planting a line of garlic near the entrance. You could also spray fox, bobcat, or wolf urine (available at garden supply stores) in the garden.