The way you say it makes it sound like you plan to work there or pass through there on a consistent/daily basis. If that's the case, the best bet would be to either ask them to set up some bike racks (who knows, they might already have them) or lockers, or ask your employer to let you keep it in the back. Also, if your mall has service entrances (particularly ones which go directly to your business), use them. It'll keep you away from the old ladies, if nothing else. The mall I used to go to had zero security in the service corridors to boot.