I agree with you, I don't want mice or snakes in my coop either! Mice carry diseases and the snakes in Missouri WILL eat eggs, chicks, and even try to kill chickens. We have these 6 ft long thin Black Racer Snakes that can get through 1/2 inch hardware cloth, so I use 1/4 inch everywhere. I plan my doors and openings to have a piece of wood that surrounds the door but gives the door a 1/2 inch edge to butt up against, and stops snakes from getting in and gives strength if a predator would push against the door. I try to walk around, both inside and outside the coop and see any tiny detail that might allow a predator to get through. Since Black Racer Snakes are amazing climbers, that means everything has to be perfect. The final layer of safety for our babies is two things. I add electrical wire around the bottom, again about 8 inches up and around the edge of the coop and run. The last item of safety is either camera with microphone or a baby monitor, or some sort of security system, at least till I can train a set of guard dogs to keep predators away LOL