Anatolian Shepherd or Great Pyrenees, but you would have to start them out supervised with the animals as a puppy. Usually the mother will teach the puppies, but you would have to do that. I would recommend you do a lot of research so you know if they are the right dog. Both breeds are independent thinkers, and will protect their charges with their lives, if need be. They are not recommended for novice owners, so if this is your first herding or guardian breed, I wouldn't recommend one. Also be aware that they can be prone to hip, elbow and thyroid problems if they are from poor bloodlines. You will need to look for a reputable breeder who is breeding for health and temperament, and preferably, who is breeding on a farm and using the parents as dual purpose, breeding and guarding.
Our current big boy is Anatolian Shepherd/border collie, and we are going to be getting a pure Anatolian for DD#3's mobility assistance service dog. Having our big boy is like having a perpetual 4 yr old, but he's a very good guardian for us. We've also been around Anatolians before, as a friend of ours has a couple, and a Great Pyrenees. We do have a breeder that we plan to go to, as well, one that imports from Turkey for genetic purposes,and has bloodlines for 3 generations, plus info on hips, elbows and thyroid for at least 2 generations.