First I don't believe those people assigned for security have to be police officers.
How many 6 and 7 year old kids drive to school and smoke?
The LEO in the small town where my grandchild goes to elementary school pulled his deputies out of the headquarters when they are assigned to desk duty and put them in the school. They do their paper work there. The school gave them an office. Now the children are protected and the officers still get their paper work done. No extra cost. That is using common sense to solve a problem on the local level. No gov. needed.
The point I make is that the policeman may also be out of position. There is no sure thing. All you can do is to minimize the damage.