6chickens in St. Charles :
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https://www.backyardchickens.com/forum/uploads/25976_hoop_chicken_cold_rainy_day.jpg
I keep trying to enlarge this detail, but wow it just won't go. There's a noisy bell hanging from the latch in case "somebody" diddles with it, there's a motion detector light aimed at the front of the coop, and the latch is secured with a stainless steel "spring clip fastener" like you'd keep on the end of a lanyard or clip to your waistband to keep your keys. The spring clip fastener requires opposing thumbs.
We used to keep a padlock, but it kept freezing and we'd have to cut the whole thing or unscrew it all just to let the chickens out. So, I think a padlock would need protection from icy moisture.
And remember, a good lock won't keep a simple wall intact. One predator pulled apart the whole fence and coop, probably a dog. They use their paws and claws much like orangutangs, they just pull things apart. So, if your coop is not built sturdy enough to withstand mean teenager prowlers and dogs, consider a good cyclone (chain-link) enclosure into which the coop will reside
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That's the same latch I use on my doors. I secure mine with those keychain-grade caribiniers. I do like the cowbell idea and will use it if the current arrangement should prove vulnerable.
My pop door, I have barrel bolts, top and bottom, operating in opposite directions. Between them is a hook with a spring-loaded catch, small enough that it would require much fiddlin, even by a coon, and is handy for latching the door to the fence wire to keep it open in a breeze.
When it gets to the big predators, there are practical limits to what you can do to keep them from tearing their way in. This from someone who endured a month of bizarre behavior from the local bears in the Catskills a few years back. The state's wildlife biologists never could explain what caused it. W lost a back door, had a refirgerator literally gutted, and the bac seat of the car ripped to shreds. No exclusion in that instance. Only repellent. 1-oz., .50cal jacketed hollow-point slugs riding in sabots though a rifled 12ga barrel.