I marked this a sad because it will screw up the dog. That said...What this sounds like is that people need to "seed" the mall with all kinds of scents nominally associated with firearms. A lot of those substances can hang around for months. Spritzing gun oils/solvents and such in entryways (especially door frames and the like, which wouldn't be cleaned as much as just floors), along grout lines, in corners, on the artificial potted plants, in the cracks, crevices, & seams of chairs/benches, would do a couple things:
1. Cause the dogs to alert on so many things that they could become "unreliable" in actually picking out true hits.
2. Desensitize the dogs to the extent that they simply WON'T alert any more because the scents will be all around them and they won't be getting the positive re-enforcement their ongoing training requires to keep them up to par.
I have no problem with doing it.