Many schools already have one. They cost about the same as a school bus. What's the problem?
I, too, thought the idea of police in the schools was a bad idea back when Bill Clinton signed off on federal money to make it happen (http://articles.latimes.com/2000/apr/16/news/mn-20323).
However, this must have made some contribution to reducing gun deaths among school children over the years.
Now that the NRA endorses the idea I’m all for it.