when I framed out my coop, I covered the entire coop and run with hardware cloth, went down 2' at a 45 degree angle. I've been using this latest coop for 4 years and I have had 1 rat get through at which point I dug down and poured 5/8th's gravel and I have never seen one since, no poison, no worry about the health of the chickens. the one downside in my design is that I did not make the eves deep, so rain water drips right along the hardware cloth where it goes into the ground and I can see that it is starting to rust. with a proper eve, galvanized hardware cloth is said to last for decades underground.
