I just thought I'd mention what we've done to add some extra security to our pop hole doors. Everyone has different situations and pet peeves. We have a lot of raccoons around here and I am not keen on fiddling with a padlock in the dark, crouched over a pop hole door, in freezing temperatures. For the pop hole door on the larger garden shed sized coop, I originally designed it so that it opens to the inside. The opening is elevated and the door was hinged on the bottom and folded down, to be used as a ramp. That way, there was no way for a raccoon to open it from the outside. It worked great and the hinged ramp adjusted to the varying levels of litter during the year. We've since replaced that door with an automatic door that uses a light sensor. It's a sliding metal plate. The battery operated pulley, door and channels it slides in are also mounted on the inside. I didn't want a raccoon to be able to just grab onto the door or the line the door is hanging from and pull it up! I also made sure the bottom edge of the automatic door plate when it's closed slides BELOW the bottom edge of the door frame opening, on the inside. The edge of the door isn't resting on the bottom of the door frame, where a raccoon claw could get under it and lift it up. You never know when some snow or litter could accidentally end up on the door frame and create a gap at the bottom of the door.