I have a lot do do with foxes and I can assure you they wont harm your dog more likely the other way around, they won't mistake your dog for a rabbit because animals go by smell and foxes are scared of dogs, one of my foxes was badly injured by a very young jack russel puppy and as for cats I found a 5 month old kitten living with my foxes 2 years ago. the only time a fox will attack is when someone or something threatens their young. If it is a family you've got under your shed they will soon be moving on to find a new territory they're not pack animals. They won't do you or your dog any harm so enjoy them while you can, I find them fascinating animals.