Liability in gun-free zones?

The recent shooting in Oregon got me thinking about liability and gun-free zones.
Our opponents have proposed limiting gun ownership by mandating gun-owners carry liability insurance (( Somehow they ignore existing renters/homeowners policies that cover accidental injury or death, including those involving guns, and which are typically quite affordable, and think that “gun insurance” would be prohibitively expensive. )).
Why don’t we, the gun-owning community, turn that around and use it to our advantage? For example, a place that’s open to the public (e.g. a university, stadium, shopping mall, theater, government building, etc.) should be partially liable for violent crimes committed on their property unless they have a “secure environment” in which all people are screened for weapons, security is provided, and unauthorized access is prohibited. Simply putting up a sign and calling it a day would no longer be sufficient.
Think of courthouses and airports: they ban guns, but have screening procedures to ensure that unauthorized people are not armed within the property, and police are readily available in case of any incident.
Can’t afford to provide screening and actual secure environments but still want to disarm law-abiding people? Then you should bear some responsibility in the event that people are victimized on your property. Don’t want to do that either? Easy: let people have the means of protecting themselves.
Naturally, private locations (e.g. homes, private businesses not serving walk-in customers, etc.) would not have such requirements.
Thoughts?