We had a police Resource officer for all of the 35 yrs. I taught in a mid-west high school. Half his salary was paid by the District, the other half by the PD. Keeping all outside doors except the main entrance locked from the outside and metal detectors would also help but most touchy-feely administrators and school boards wouldn't want parents to get the idea schools aren't safe. The reality of modern life is that no place is safe. Parents should demand minimum safe-guards.