We have padlocks as well as the sliding knob in the groove type lock. The first set rusted, so we got another set of padlocks, this time longer armed locks. The nest boxes open inside the tool shed, and we have carabiners on those.
We actually have a hasp and padlock. Of course the key is kept hanging up a couple of feet above the door. We are mostly concerned with the coons figuring out how to open any latches. I figure that if the coon figures out the key and lock, we have more to worry about than the chickens lol.