You did not say how you would be hunting foxes but for called foxes I've found it very hard to beat an accurate 22 Magnum. Out to 125yds or so it is deadly on foxes and never ruins fur no matter the shot angle or distance.
For something with a little more range I'd be thinking .17 Fireball with 20gr V-maxes. That may well be the quintessential fox fur load........
X-VERMINATOR