I wrote this piece on a FB page 5 years ago. I still like my idea.

Every "gun free-zone" should allow for the volunteering of staff to become First Immediate Retaliation Enforcers (aka FIRE). The FIRE team would be trained individuals who are subject to annual psychological evals. They would have access to hidden lock boxes with biometric security and pincode. Inside would be a handgun easily concealed and used at a later time if necessary (hostage situation), a charged in-ear radio system for comms with other FIRE teams and external emergency teams, and some zip ties to restrain shooters. The goal would be to decrease the body count and to stop the incident from progressing.
Key points to this plan:
-trained individuals who are subjected to psych evals.
-hidden lockboxes with gun, ammo, radio, and restraints
-Plan of action in an active shooter situation
-Practice for FIRE team
-Silent alarm system
-regular drills
-anonymous FIRE team members