I also leave the coop door open day and night. I'm not a morning person so it's usually 10 a.m. before I get out there and let them out of their run. Even then they are pacing in front of the gate, tripping over one another. If they were locked up in their coop they would probably be killing each other. I've never had a problem with predators but I do understand that is a risk I take. My theory/reasoning also goes something like this - if a predator did get in the coop I would rather that some of the chickens could at least escape and not be locked in with the killer. Again, thank the Lord, I haven't had that theory tested. Mine also free range all day long and by leaving the coop open, they come back when they need to lay an egg and then go back to free ranging. I guess you could say we have an "open door policy" around here. They come and go as they please. I do close and lock the run gate at night after they've all gone in.