I have a fly trap hanging in the nectarine tree outside the run and I don't have flies in the coop or run. I clean the coop daily (I have a tiny flock and a tiny coop) and clean the run weekly. I'm sure that helps, but even the watermelon rinds don't draw flies. I'm kind of surprised, because we still have a problem with flies coming into the house. It doesn't help that we have three dogs. Maybe that's the secret to a fly-free chicken run - a bigger draw for them on your lawn. We pick up dog poo daily too, but with three of them, there's always some we miss.