I have had flystrike in my flock twice now. The first one was too far gone and had to be culled, the second one I was able to save. Both of these chickens had very poopy butts and the chicken coop had a lot of flies. After my second hen I decided to switch to sand in the coop, and that eliminated almost all flies in the coop. In the run I still have just dirt, but I know people put sand in there too. I also got some Elector PSP, which was more of a panic impulse buy since the sand keeps the flies away anyhow, but you can spray that directly on the chicken if you're willing to spend that amount of money. My chickens with poopy butts don't like to be messed with either, so I will just spray that stuff directly on the chickens' butt. It's less stressful for them and me both. I will also spray it around the coop because why not, extra protection. Just be sure to follow the directions.