How would you prevent anyone from entering the grounds at any point besides the ECP? Fencing? How high? Would it have barbed wire or razor ribbon?
What would prevent your armed guard from being sniped at the beginning of an attack?
What prevents the gate guard at Elgin from being sniped?
Seriously speaking, I was in first grade in Europe when operation desert storm kicked off, at a DOD school. The school was surrounded by a 10 foot brick wall, and at the time the two entrances were a big gate for vehicles and a small gate for foot traffic. I took the bus so I can only remember the big gate, a large painted steel deal on a motorized tract that was only opened when the busses came/left. On the outside of the gate there was an armed uniformed guard, and either up or across the street two plainsclothes officers in vests with rifles and windows that were a couple inches thick(they'd roll them down when they smoked). All were provided by the host nations federal police. They also provided a guy for each bus, with one plains clothed marine per bus as well. Our teachers also made time to tell us to watch out for unattended bags/boxes/packages, and that if we saw one to immidiatly notify an adult. Of course, that was a foreign country, while the United States was at war, and all the students were defendants of department of defense personal.
I'm not saying that's what we need in every school in America. I'm not saying we could afford anything like that. Im just saying I've seen a school take security seriously before, and that's what it looked like.