As is, those who impose a "Gun Free Zone" are not held responsible for those entering their Zone... Those entering such Zone have no assurance that everyone entering is in fact unarmed.
Those who impose a "Gun Free Zone" need to be legally responsible in providing such security that everyone entering is in fact unarmed and the ability to deal with those who would try to enter the GFZ armed..
In short, if anyone would take away the right of citizens to adequately provide themselves with self protection in a "Gun Free Zone", then that person or entity has to take over that responsibility for them..