Foxes are not an exclusively nocturnal hunter/feeder like some other predators. They will hunt whenever they perceive that it is going to benefit them the most. They are also among the most clever at overcoming any protections you have in place. They can dig, burrow, climb, manipulate locks and latches much like raccoons and seemingly pass through solid walls and fences. They will stalk and attack your flock with you standing there watching as if to say "so, do something already human". Your guard must always be up if you have Foxes around...that and your rifle loaded.
X50. The only fox loss we've had was middle of the afternoon, in the horse pasture WITH the horses, in front of the house, with my kids outside.
Donkeys are great livestock guardians, as they will actively seek out and kill canines. If I had more of an issue, I'd get one. But I have 5 dogs, too, who may not be smart enough to not try and play with the donkey......