In my little 30'x30' fenced garden I've been having issues this year with "nibbled" seedlings and small plants.
The setup:
My fence is 3' high, with wire rectangles of 1.5" x 2.75", it rests on a bed of weedblock fabric and cardboard and is stapled to the ground. There is no evidence of a hole or other sort of breach.
The affected produce:
My row of cucumbers all had their leaves eaten roughly 1-2 weeks after sprouting. My second planting was covered with a floating cover which was stapled down; I've lost half the row so far - nibbled to the stem. The lone eggplant in this garden got defoliated (southwest corner) oddly enough my separate vinyl fenced eggplant bed ~50' away is completely unscathed. My carrots sprouted and were wiped out at about the "emerging fern" stage. I lost the watermelon plants I put in where the carrots were, it appeared like a low-bodied animal ate around the plant as there was a circular shape left in the dirt around both eaten plants.
So far unaffected produce:
Tomatoes, Beans, Peas, Lettuce, Potatoes.
The suspects:
My first inking was a groundhog, there are a few "residents" in the neighborhood, I've only seen one this year around my property but don't see how one could fit inside the fence without burrowing.
I set out the Havaharts and so far have caught 6 squirrels (in garden) and one possum (outside of garden). The squirrels love to futz with my potato mounds and otherwise cause mischief but I've never seen them eat anything that's not a berry. There is a cherry tree (past), mulberry tree (ripe) and an upcoming bounty of blackberries in the yard.
My next suspect would be a rabbit, fits through the fence, not a likely Havahart victim, enjoys fresh leafy stuff like carrot tops. There was a roadkilled rabbit in my side hedges about two months ago, so it's likely that there is a family nearby.
Aside from that, I'm out of ideas and way behind on production.
The layout (I know... not ideal at all)
I'm in suburbia and can't camp and blast, so it's traps, repellent or suck it up.