The Air Force is leading the way on active shooter defense. Allowing concealed carry on base, having unit marshals that carry so every building has defensive shooters, and allowing retired LEOSO concealed carry on many bases. I know its fun to disparage them, but they’re getting this right.
Chairs are my favorite for fantasy fight-back. They can be wicked. I'm a bad fantasizer, though. I keep thinking, "No, that wouldn't work."