I'm building a large run for chickens (currently chicks) and I'm almost done, but can't figure out what to use for flooring. I'll be using sand inside of the coop (when they're old enough) but I was not sure as to leaving the run as dirt so they aren't bored or put sand in for ease of cleaning? My family is very busy and we have predators in our suburban neighborhood, so they will not free range as they much as they might like.