I agree with armed school personnel including teachers and janitors if they can qualify.
Punishment, that is the next step in deterrence. I know Texas is likely to execute such criminals. My ideal would be to speed the process up to weeks from conviction to death. Add onto that a public execution, with schools required to show this to their students nationwide. Make sure death is drilled into their heads as both real, and permanent. A lot of people play so many video games, and are disconnected from the harvest of food, that they think they just hit “RESET” and begin again.
Works for me.