Actually, you can set out ivermectin in raw hamburger and that will take care of mange. We had a mangy fox in our neighborhood a couple of years ago and a tube of ivermec in about six meatballs made a huge difference. Mange can kill a fox otherwise.
I now put out baits every eight weeks to keep the foxes clear of mange- they managed to transmit it to my dogs once, who then had to be treated, so I figure "treat the source" is the better option.
Foxes have a sort of rank smell, you should be able to tell if one is living in your hole. They also like to leave their small black poops in prominent locations- I guess it's a territory marker?