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

So far, so good this year. But it could change overnight. In years past, groundhogs. Even though I have a four foot high fence that's also underground 2 feet. Groundhogs can climb, and babies can fit through the small openings. Last year I had loose chickenwire attached to the top of the fence that bends outward. Supposedly this discourages them b/c they can't negotiate the bendy, loose wire. We had way too much rain this month - 9 inches in the first week of June, so that meant a bit of rot of seedlings and seeds. But it's been drier since and things have started to grow. Still, lately we get really heavy downpours instead of nice steady rains, and this is hard on the gardens. The other thing that I have never been able to deal with is the early blight on tomatoes. My garden isn't big enough to constantly rotate them, plus parts are too shady for tomatoes. I try my best with a heavy mulch of hay to prevent, as much as possible, splashing on plants from rain (the blight lives in the soil), and this year I'm also spraying with neem. We'll see what happens.