ten years. Think about the impact even one incident of corruption would carry if it involved school children.
According to wikipedia, TSA employed 53,000 people in 2011, that's only roughly half of the number of guards needed to man a single guard per school in this country. What about college campuses? VT has had two rampages now IIRC.
I'm not going to mention how effective they might be because sometimes, like the massacre on the military base in Texas they aren't. Sometimes, like the averted massacres in San Antonio recently, they are. Armed guards are inconsistently effective. Think for a minute about the worst case scenario of a shootout in a school. Think about the last time you have seen a police video of an officer being