Rhodesian Ridgeback. Smart, tough, athletic. They are big enough to deter most casual 2 or 4 legged predators but for a determined predator you will need to be able to back your dog up with a weapon. Also I have never owned a mastiff type of dog but I would be leary of taking a dog on 5-10 mile hikes that would be too big for me to carry if it got hurt. I could put one of my dogs into a tarp and hike back to camp if I really had to. I have no idea what I would do if I owned a CO or Corso that got snake bit, a broken leg or had gotten chewed up by a pack of coydogs.