I would recommend talking to the police department in your town about providing information on how to handle this and similar situations. You may invite them to do a presentation, but because you have 29 stores, you will proabably want to have a powerpoint or some other deliverable that can be passed out to your store managers to disseminate to employees.
If for any reason having the police provide this information is not possible, then you need to develop a plan yourself. Consider the fact that employee safety should rank above merchandise or cash on hand. Create a protocol and teach your employees.