Answer: These can both cause lots of damage in the garden. For rabbits, the most effective long term control is a wire mesh fence about thirty inches tall and anchored at the bottom so they can't duck under it. However, many gardeners report success with using repellent sprays, either homemade garlic/pepper based or commercial such as "Get Away" brand, or predator urine. ( Another deterrent may be a pet dog on patrol.) Still others report that onions and members of the onion family such as chives seem to repel them if interplanted in the garden.
Woodchucks, however, can be very dangerous animals especially if they are in an area where they might contact people. Although the fencing and other suggestions might keep them away from your garden, I would suggest you call in a professional to trap and remove the groundhog. (In fact, they are so unpredictable and potentially dangerous I would not suggest you try to trap it yourself.)
Q&A Library Searching Tips