We had our chicken door hinged on the bottom so they could walk out on it, but every time I went to shut it, it had droppings all over it and shavings around the hinges. Now we have the hinges on the top and I positioned a 1/2"thick by 3"by 8"long piece of wood so when it is perfectly straight up and down the door opens. If the wood is just a little bit to either side the door will not open. When I close the door I make sure that wood is a little below horizontal so that coon would have to lift that piece of wood up and then to the left, the wood doesn't move easy either.
We did have a coon get one of our hens one night, she was being a pain and picking on every body all day. They have a porch on the coop so they can be outside when the weather is a little bad and she didn't want to go in that night. The porch was all closed up except the space between the rafters, (which I had forgotten about)the coop is at least 2 and a 1/2' off the ground, that coon stretched up no problem. I heard her scream but by the time I got there the coon had killed her, so at 3AM I was out cleaning up the mess and putting that piece of wood on the small chicken door from the coop to the porch. We were very lucky that coon didn't get into the coop. We do have a door that opens down from the porch to the ground, but it has wire on it so droppings don't stay and small strips of wood for the chickens to walk on. We do have to keep the hinged opening cleaned or it doesn't shut right, but it is easier to keep clean. That very next day the space between the rafters was filled in. We've chased the coons off a couple times and are very aware of the time of day, as soon as the sun starts to set all the chickens are inside for the night. Training them to come when you call is very good and important when you have predators around.
Hope you can keep those coons away,
Cindy