Charise, here is a good site to read over. This individual has been breeding for well over 20 years.

As he states, the "aggressiveness" is well documented and known in the breed. Although should not be considered aggressive as much as protective. This is what they do.

You should consider continuous obedience/socializing training. From reading the article, it sounds like he is doing something that is natural to him. Do get him nuetered to minimize the intensity of the protectiveness in him. This will help immensely.

Good luck and keep us posted.

greatpyrenees