For those of you that do not free range your ducks exclusively, what do you use for the ground in their outdoor area? It seems that pea gravel, sand, and bare earth seem to be the most common. Have you found something that you use that is extraordinary? We are building our pen on a slight slope, and I'm thinking of building a small retaining wall around where the pond will be and filling it with pea gravel to help with the filth and drainage. Unsure what to use on the "covered" area's ground. Perhaps sand will be a good option so they have some grit and I'll be able to scoop poop like cat litter? Let's hear what your set up is!