This may be slightly off topic, but...
Our SRO's were a valuable asset when I was in high school. Not only for protective reasons, but they were a very positive influence and good role models for the students. Occasionally they would even step in as substitute teachers. Although they didn't stick to the teacher's lesson plan, the class would always be engaged in productive conversation about things like the Constitution and civic responsibility rather than sleeping through another boring movie as with a regular substitute. They were well respected, and there's no doubt that we were all safer with them in the building.
I think this is a great idea for multiple reasons, including protecting our kids.