Ok, speaking as someone who, along with the wife is HEAVILY involved in the dog world, the first thing you need to do is, research which you've already started, and then find an internet board devoted to the breeds you find interesting. Then ask lots of questions.
Truth is, ANY dog can be trained for protection. Even those lovable golden retrievers. Certain dogs have been bred for specific traits, but you have to understand what those traits are and what possible problems there could be. Anatolians for example ARE excellent guardians. They'll guard you and your family from EVERYTHING. Including your friends and neighbors.
All dogs have quirks or personality traits common to their breed that can make them difficult for some people to handle/work with or a joy to own. Ya gots ta know before ya buy.
With large aggressive breeds, it's important to buy for a responsible breeder to make sure you get one that has the right temperament. Responsible means that you'll probably have to go thru some interrogation to determine if you're the right sort of people for the dog, and it means that the breeder will not only take the dog back if there is a problem, they'll insist on it.
Other good breeds to look at would be Rottweiler, and Cane Corso. We have 6 Rotts guesting at our farm right now and they are really something. Friendly as can be, but their growl! Wow. Even when you're playing you find yourself double checking to make sure that
he's still playing too! Even their owner, who's a breeder gets fooled sometimes.
My wife, and the breeder I mentioned are on tilted too. Let me know if you want more info and they could help you out. I'm sure there's other dog people on the board too though!
Hope this helps