Wow, what a gorgeous dog - that's a breed I've never heard of and I thought I knew them all. The description scared me, though, because I had a very bad experience with a "good guard dog" type. My Neapolitan Mastiff took her duties MUCH too seriously and we really had to watch her like a hawk. Even so, she wanted to hurt anyone or anything that was not part of the immediate family. I had hoped that socializing her from a very young age would help so we did obedience classes and took her lots of places with us but it was soon evident that having her out in public was much too risky. She immediately claimed any place we were in for 10 minutes or more "ours" and wouldn't let anyone else move. Beautiful, loving dog, but a real handful and stressful to own. My great dane is large and intimidating but has NO desire to hurt anything . . . a real gentle giant.
Good luck with him - I'm betting you're a dog savvy person and will be able to raise him to be a good guard dog while not being a danger or liability to those he's supposed to accept.
Sue