My coop sits right on the ground and doesn't have a floor. As it doesn't rain here in summer, I didn't have any problems with that for months - the ground in the coop was nice, dry, fluffy earth. Now, after a few hearty winter rains, the ground is soaking and muddy. Also inside the coop, it's just seeping in. My poor chickens are wading through the mud and I get involuntarily mud brown eggs instead of white ones... Even when it doesn't rain the stuff doesn't dry because it's too cold. What's the best material to put in to create a dry surface on the mud? Straw? Wood chips? Sand?