A 45gr Barnes TSX does this. Drops foxes and coyotes with authority and leaves very small exit holes. Always 100% penetration.Fox will be the problem, as they are very fragile, hide wise. I would choose a .223 with a tough 55 gr bullet. As in a soft point Sierra and not a plastic tipped bullet. Plan on an exit hole, but not to big with a bullet that gives limited expansion. Been there and done that! A .5 to 1" exit is what you want. Easily sewn up. A 5" exit hole, not so much. Good luck with your adventure.
Paul