I remember the river cottage ladder and coop -I think I have it in a book here somewhere. It was a small coop about 6 feet or more high, set on a single post. The ladder at the front was a simple single spar with the steps nailed on. Very flimsy deliberately so that the weight of a fox would tip it over. I remember thinking a mink wouldn't tip it. To clean out the coop and collect eggs there was a ladder to the back. The chickens had to be trained to use it and heavy breeds would struggle -no chance with our Orpingtons. Lot of fuss to avoid shutting the pop-hole at night I think.
Seen another variation with a see-saw ladder. The ladder is long and the pivot is offset so that the weight of a chicken won't upset it, but a fox would get past the pivot and the ladder would tip up, sending the fox to the ground. Again mink, cats or rats wouldn't be affected.
We had one fox strike in the UK at dusk, just before we went down to shut the pop-hole. The hen was attacked on the way back to the coop, so any sort of ladder would have made no difference. The other two strikes were during the day.