Agreed with Aart. IMO, DLM is best for almost all applications. My limited exposure to sand is this: You might like it for a while. But, it requires constant maintenance: raking poo out of it on a regular, if not daily basis. Even daily raking will not remove all feces. There will be particles that sift down into the sand. when the sand gets wet, that will further enable the poo to mix in with the sand. Eventually, you will have a fecal laden mix that will reek every time it gets damp. In dry windy conditions, the fecal dust will disperse into the surrounding air.
If the area where your coop and run are is prone to standing water, that MUST be dealt with. A wet chicken yard is an invitation to coccidiosis, internal parasites and other disease. cover the run, add gutters, drainage tile, pea stone, drainage ditches to direct water away from the area.
