Have you thought of using straw instead of wood chips. My girls love scratching through it. We live on the Oregon coast and in the rainy season this really helps keep the ground dryer. We use to fight with mud in the past. I've been using straw for 2 years now and never have cleaned it out of the run. The girls just seem to break it down to pretty much to nothing and then we add another bail of straw for them. I do rack it around once in awhile to keep it leveled out. This seems to be working good for us. Just my thoughts. Everyone has to find out what's going to work best for them.