We are almost done with are new coop. The barn is designed with two 10X18 FOOT BARNS ON EACH END WITH A COVERED ROOF RUN IN BETWEEN THEM.The run is double the square ft. of barns,.We are pouring concrete in barn and run.I live in Mi. so have problems with predators and digging.. My ques. is do I put sand in the whole thing?Barns and run? Or just concrete and sand in the barns and leave run dirt since they will only be out there in the day? .