Saw your post after I posted my message. This doesn't fly in Oklahoma. We've done our research and have consulted attorneys on the matter. We're more liable for any harm caused by concealed carry we willingly allow on our property versus having gun buster signs and someone (employee or otherwise) busting in and shooting up the place. Having employees, tenants, coworkers, ect sign contracts or non-liability agreements doesn't hold any water. One of our own tenants was pushing for us to allow him to carry concealed and even offered to sign a non-liability agreement. After he did his own research on the matter, he came to the same conclusion that our lawyers did and dropped the matter. Us allowing him to carry would make us liable for him with his firearm with or without a non-liability agreement.
If anything, the non-liability agreement would make you even more directly liable for any damages because, in effect, it serves as you sponsoring that particular individual to carry when no one else can't. You're better off just removing the gun buster signs and letting everyone carry in that case.
Even if this is true, regarding the law, as a business owner, I would still have to consider the overall odds. While neither is very likely, I think it is much more likely that a criminal ignores your policies and opens fire than it would be for a concealed carry permit holder to open fire. Therefore, it would actually behove you to allow concealed carry.