Unless everybody who enters, including off-duty LEO's, goes through airport-esque security clearance, that rule is a pipe dream . . .
These Tanner shows require every firearm, regardless of ccw, vendor, "joe citizen" that enters to be zip-tied- no exceptions. Lots of signage every where advising so.
Here's a link from the local FOX station with some more info:
Man injured in accidental shooting at Tanner Gun Show | FOX31 Denver