DogDaze-- The .204 Ruger is a great coyote round in my limited experience with it. I have only shot two coyotes with mine and I was using my prairie dog load--the 32 gr. V-Max leaving the muzzle at 4,255 fps. Both shots were pretty much with the coyotes facing me, so there was little or no fur damage. My coyote load is going to be the 35 gr. Berger FB HP bullet with a muzzle velocity of around 4,200 fps. We don't have too many red fox up in this country since the coyotes moved in.
I'm afraid that the .204 Ruger, with fullhouse loads is going to be real tough on fox hides though, unless you are lucky enough to shoot them looking dead straight at you. The skin on a fox is pretty darn thin and if you are shooting a 32 gr. V-Max at 4,200 fps or a 35 gr. Berger at 4,000+ fps, or a 40 gr. bullet at 3,800 or 3,900 fps, I'm afraid that broadside shots are going to make a hole that your wife won't be real pleased about.
Perhaps, if you loaded some .204 Ruger shells down to the 3,000 fps range, you might find they would work pretty good on fox. Trick is, though, to find a load that will shoot to a similar point of aim with the fullhouse load and the slower load. Maybe the solution is to carry two rifles LOL /ubbthreads/images/graemlins/laugh.gif