I use dogs and fencing very effectively against foxes. My elder dogs first encounter against a fox was when dog was about 6 months old and was made easier by fox being focused on a cockerel he was trying to steal. Dog ran up on fox from behind and actually had a hold of a bit before fox managed to free itself and escape. Dog was bitten in process. Since then we have killed two foxes and fences may make the dog's job easier. The fencing made up of perimeters of simply high tensile hot-wire and electrified causes fox to take predictable routes the dogs can take advantage of to intercept fox. Fencing, even though semipermeable to chickens still provides some measure of cover until the dogs can get there. I use two dogs which is really handy with fast evasive bad guys like a fox.