I would want to think about installing some sensors in those doors that are not main entrance doors. Either a buzzer or a flashing light goes off when those doors are open.  IF someone is going to prop open a door, have it so someone is alerted and can investigate. 

The thought of installing a camera - with a feed back to the main office - at those doors crossed my mind. I don't know how that would go over with a private Mennonite school.  It might be something to suggest. That would allow monitoring whom goes in and out of those non-main entrance doors.