Electric fencing wire and a good roof will probably do.
A word in defence of foxes. They don't kill for the fun of it. Just like dogs and wolves, they will hide or bury what they can't eat immediately, and when they are presented with a glut of prey, they will kill what they can when they can.They have to survive on chance kills; there is no guarantee , in the wild, that they will find enough to support them and the young every day, so they have adapted to storing an excess and going hungry at other times. We humans have, unwittingly, supplied them with the occasional bonanza.