I have boards that go a few inches into the dirt. The inside of the pen I seeded with grass like a lawn. The grass has roots deep enough to keep the dirt down. I have a small pit of dirt for them to take dust bathes in. I water the grass when the dirt gets dry and I try to push the grass long enough so it will encourage the roots to grow deep enough to hold the dirt down and so that when they chicken scratch or eat the grass the roots can stay in the dirt hopefully. I have never mowed or cut the grass so my grass lodged over and dropped seeds and now new grass is coming up and the old grass is decomposing. If you water it enough the grass won't get fried from too much nutrients nor will their be much poop on the grass since it will be absorbed quickly when you flood the grass.
