The Federal 3" copper coated lead BB's should do a great job on foxes. I have killed a bunch of coyotes with that load.
The Hevi-Shot waterfowl 3" #2's or "B" load should work great also if you want to pay more money for them. I counted the pellets in a Hevi-Shot "B" load and there was 71 pellets in it.
The Hevi-Shot waterfowl loads are cheaper than the Dead Coyote loads are.
The Remington HD Ultimate Home Defense 2-3/4" BB loads that Bass Pro Shops has on sale is a GREAT load for the money if they still have them. There was 59 pellets in the shell I opened up and they are $9.98 per box of 10 shells. The original price was $24.00 per box.