I'll give you same advice as other mystery hole critter thread. Get yourself some muck or fine mud and lay it in front of one of the larger holes. Anything in or out of that hole will leave a track. Muskrat tracks are fairly distinctive. And they normally have hidden entrances, like beavers, even underwater, where most of them are. They also have dining chambers besides their dens. Those are more above water lines and more frequently found by dogs and predators. My favorite muskrat is one with a red dot on his head.
