Olivia, I'll hunt the fox for you, if you like. In all seriousness, any of these predators are bad news for cats and dogs. Possums, racoons, wolves, coyotes, owls, hawks, and foxes will predate upon smaller mammals, which unfortunately includes most cats and dog breeds smaller than 30 lbs. Fences are not sufficient barriers for keeping out predatory wildlife. Unless you're going to trap and relocate the fox to a significant distance (I'm talking like 800 miles) the fox will come back. Foxes aren't cute despite Disney's attempts to make them appealing - they are destructive vermin that tend to carry all sorts of parasites and diseases (including rabies and ticks).