I've shot a lot of Fox. Pick your shot, between the shoulder and the guts. The object is through the ribs and hopefully the bullet makes it all the way through without tumbling or fragmenting. Keeping a picture in your mind of where your bullet is going in and where it is likely to exit also helps. Gut shooting a Fox is almost guaranteed to make a mess and there is something about the smell of a gut shot Fox, Yote, Cat or most any predator for that matter, that gags me up pretty bad, I avoid it. Sometimes a bullet just catches a rib the wrong way and it can tear things up some, though not often.

I think hollow points or similar bullets may be a large part of the issue. I've used a .308 Core Lokt, 7x57 pointed soft point and a .222 pointed soft point on Fox without much issue and surprisingly the larger calibers often do less damage than the .222. Best guess is it is hole in and hole out before the bullet has a chance to deform/expand any or much. I've never tried FMJ and gave up on hollow points quick in my .222. Shot placement, using the right bullet and excessive damage is negligible.

I think what the trick is, with high velocity bullets, is to use a bullet less likely to deform or fragment a lot if/when it hits a rib. And to shoot them through the lungs so the fluid wake (hydro static shock) is minimized.

For decades here Fox was shoot them when you see them, they were considered overpopulated. I'd take one at the end of my Deer or Hog hunt. I shot one young fox, not much bigger than a house Cat, side shot through the ribs/lungs with a .308 and it was hole in and hole out, no real damage to speak of.