Eaten Alive!

My little garden project was off to a good start. But then, after less than two weeks, I noticed something had been eating some of my plants!

First we have the Rainbow Chard, with yellowed, spotty leaves, and what appear to be snail or caterpillar holes?

Then we have the spinach, totally getting discolored. I'm told this may be from overwatering, so we've eased off of the watering (Will and I are both chronic overwaterers). Many people have mentioned that yellowing is a sign of a nitrogen deficiency, but the compost we used when planting should've prevented that -- I'm hoping it's because the overwatering caused an imbalance in the nitrogen level of the soil (I read about that online), and once we let it dry out a little bit, it'll rebalance?

What can I do about the pests, though? They don't seem to be attacking anything else, and these two plants aren't even next to each other (though they do have similar leaf-styles? could that be why they are specifically being targeted?). Damn bugs eating my plants!

The other pest (not pictured) is a fat little squirrel, whom I have actually caught red handed, stealing strawberries off our one lonely strawberry plant. There were only three berries, and only one was close to turning red enough to pick, but he doesn't seem to care. What do you do about squirrels on the ground? I've heard of tying tinsel in fruit trees to ward off squirrels, but can I tie tinsel to the strawberry plant?

Help me, oh garden-savvy friends! You're my only hope!