In South Louisiana many of the "bulldogs" and bulldog crosses are used as catch dogs and hunting dogs for dangerous game (feral pigs & bears primarily). While not true shepherd dogs they will be Hades on four legs on anything that enters the property - assuming it crawls on all fours. Of course, one would have to train it not to harass the livestock. Perhaps a cross between a Catahoula and an American Bulldog or Pit Bull would suit your purposes. These can be found rather easily and most (if not all) are working dog stock. Good luck.