A change

Good Morning!!! I have a long story and cutting it short. My husband and I have our lady hens and they have free range since we have had them. We thank God never had a preditor in our area except recently with the new renters across our street. Their dog we believe killed one and two more are missing..... i will leave the conclusion there...... anyway we have now placed them back in there coop and now the bottom grassy area is bare. I have a self feeder but is there anything else to put in for the bottom. I'm planing on making the fenced coop area moblie to move it around the yard. I'm just worried are they getting enough food??? Any help would be appreicated.