What is the most difficult pest you deal with in your garden?

Squirrels are my biggest pest right now...not so much stealing vegetables, but digging holes in the garden...uprooting beets, onions, and radishes. I come home from work and find any number of holes in the ground. I'm just lucky they haven't taken out a tomato plant yet. This is the first year I've experienced this, so I know what the squirrels smell or why they're digging, but it's becoming a real pain. :-(