I like your tarp idea yawningreyhound! Something I found helped with mice getting into the feed (you have only mentioned them in the water but nonetheless...) I mixed a bunch of cayenne pepper into the feed for a while and the mice decided to try food that had less spice in it

I also set live traps in the coop and was very busy for a while deporting the unwanted critters to another pasture area. I think watching the hens destroying straw bales, cabbage treats etc is very entertaining. Even more so if you put it just barely out of their reach and they have to jump a bit to get a decent bite LOL