My chickens used to free range until Mr Fox got too familiar, so now they are all in a very large pen, about 12m x 7m. The walls of the pen are 6ft high, with the bottoms buried to stop the fox digging. So far so good - the fox hasn't got in. However, the chickens are still getting out, and the fox takes them this way. I have lost 5 this year this way. We live in an ancient forest, so there are trees in the pen and outside of it. I thought they were maybe flying into the trees and getting out that way, so I have removed all of the lower branches. They are still getting out. The size of the pen means I can't put a roof on it - I did once before and a snowfall caused the whole lot to collapse in a mess.
So what can I do next? I'm fed up of chasing them round each morning, and even more fed up of finding piles of feathers.