I agree with Jan, squirrels are my biggest problem. I have one I want to strangle. He's dug up my melons numerous times, rolled all over my flower & veggie seedlings in my patio greenhouse & is perpetually pelting the garden with half eaten apples from my apple tree.
My next biggest problem is skunks. I'll take a possum any day over a skunk! They are digging up everything I plant in my front yard. They just love freshly dug dirt. I am not looking forward to planting (& replanting) bulbs in the Fall.