Some fox are lighter built than some feral cats. They come apart fairly easy and don't need a lot of killing - hitting the shoulder bones on them with fragile bullets can cause a mess, as you've found - sometimes w/o hitting the bones. That said I wouldn't recommend a 22 LR. 22 mag with the heavier bullets & 17 HMR with the heavier bullets should work well to 150 yards or so if you have the rest, accuracy and ability to do so in the field. 22 Hornet will work very well too, and may be the ideal fox round to 150+ yards in standard calibers. If you can reload, tougher, heavier bullets in any caliber should help reduce destruction, especially if loaded slower. Stay away from fmj's - you'll lose animals eventually with them. 222, 223 and up are (as you have found) a bit destructive to critters of this size unless downloaded. 17 Ackley Hornet is ideal, but a wildcat as stated above. 17 fireball is probably good, and better if downloaded a bit. 17 Rem will work, but probably should be reduced a bit in velocity for fox. Again, the frangible bullets like the v-max you're shooting can REALLY make a mess of fox-sized critters. And stay off the bones with your shot placement for reduced splashes going in. Anything that will not blow up a fox maybe a bit lite for killing coyotes reliably if you get a coyote in - again shot placement is key and try to stay off the bones to get to the "goods" on both.