Sand, sand, and sand. ALL of my runs, coops, sheep stalls and everything have a 6-8 layer of pure sand in them. It is GREAT to say the least. The sand will pull all the moisture out of the poop and it will disinigrate, any rain and wetness goes to the bottom of the sand keeping feet and feathers dry, and they LOVE to dust bathe in the warm sand! It also keeps the flies away in the summer, you are not slopping around in poop soup, and it is just great all around. I get a dump truck load every fall for $45 dollars and we also fill in any low spots too that may hold water in the winter (like well used walkways and such). If you should get a build up of poop, or a spot that gets cakey, all you have to do is run the rake over it and your good.