I have kept a few chickens for many years in a rural area where there are foxes, badgers, otters, polecats and buzzards.
In twenty five years have lost a few hens to predators because I have not shut them in at night, except for the loss of four hens attacked by a buzzard.
The hens have a wooden shed to roost in and a wire run for winter and when it's too wet to forage outside.
They enter the run from outside via a pophole or the door and the roosting shed via a pop hole about 450mm from the ground which has a curtain made from polythene strips similar to those on industrial buildings but on a miniature scale. This was intended to keep sparrows out of the hen house. The hens soon learnt to go through it.
Early last year a predator, I think a fox, chewed through the wire netting around the run and made a neat body sized hole. It did not take any hens. Since then I have not shut the hens in at night.
Two days ago I put a broody hen into a separate pen beside the run and last night a fox chewed through the wire netting and took the hen. I found some reddish fur on the wire. Again no losses in the roosting shed.
The only explanation I have for this is that the polythene curtain deters foxes from entering the hen house. I know that foxes are very wary of anything that could be a trap or snare and would be suspicious of anything unfamiliar.