I'd be curious to see an update from the writer. We tried sand and found it too dry; did not like it at all. We accidentally stumbled upon something that's worked perfectly for us-river rock/pebbles. We initially used them to cover fencing we had laid on the floor to prevent predators, but it has an added benefit--the poo washes out from under it when it rains. The area is not a flood area, but does retain just enough water during a good rain to naturally rinse the rocks as it flows away. OFC this wouldn't work in a non-natural flooring situation, but works well for us. In the tray under the coop itself, we use coffee grounds and those work well too.
