What kind of dirt should I used for their box for their dirt baths? I have a coop that has access to the regular ground, they ate all the grass under it but theres also poop and hay on the ground outside in the area they walk around. Do i leave it? pick it up and keep just dirt and put a box of sand for them or the ground and no box? they really can't roll around in that cuz its hard. I'm just wanna keep em happy and healthy. Thanks in advance.