We have two compost piles. One is just leaves, grass clippings, twigs, etc.--no food. That one is an open pile. The other compost pile is for vegetable scraps from the kitchen and rotten veggies from the garden--but no animal products. The second one is in a sealed bin which we bought from Metro for $25--I think its called an Earth Machine. If that stuff wasn't sealed we'd probably have more pests--raccoons, rats, whatever.Maybe I'll put the compost in a garbage can or something...
Maybe there was a large rat population in your vicinity already and then they lost a food source, so they found your garden. Really odd that you would have so many rats being so obvious, climbing vines, getting run over in the street....