What I did was attached deer netting to three sides of the fencing at the end of the run about 14'' off the ground. Our run is long and narrow about 50'X10'. I put 2 short wide pots and filled them half way with a soil/compost mix under the netting to help support the net when the chickens walk on it. The side of the netting that is not attached to fence has rocks weighing it down so the chickens cannot get underneath it. I spread a "chicken pasture" seed mix and voila! The point is that chickens can eat the greens as they grow but can't scratch them out of the ground. I got the idea from a customer at the nursery who made a 2'X6' frame for this purpose. I had this setup for about 2 years and it worked well. I recently tore it down as the native weeds had taken over. I am letting the birds "renovate" the area before I start over again. Here is the only pic I could find. Notice the chicken on the left is elevated in comparison to the birds on the right.