I have said this for years. The "school" should be in Westchester (not in the middle of Central Park which is THE dumbest thing x-writers have done in years), but the real campus should be somewhere else. Use the mansion as the face of the school, but have the students all off at the real campus in say Genosha, Canada, or the American southwest or any place more isolated with teleporters liking the two. They could not only fortify the campus more if they were isolated but have more room to let the kids really learn how to use their powers. Plus if they were not around so many people them fortifying the campus would not freak people out and make them think think the mutants are preparing for something.
It has been shown too many times that them trying to follow Xaviers "dream" and be totally open with general public just ends up in kids getting killed.