Tom asked 

But how can one stop it if it gets started?


If your hives have ventilation( mine are D.E hives) you can close the front with a screen, or completely if needed - I have done this in the past successfully.  The bees/hive fared well, and after 1 day, I opened the hive, and restricted the opening until visiting bees decreased comfortably.  Of course, I am assuming that you will get your complete bee suite on for this procedure.  

And about avoiding robbing?  Be careful when you rob the hive yourself.  I robbed my hive once in too hot, too dry weather during a blossom dearth and immediately following the neighboring hives dropped by for a little nip of honey from the robbed hive.  But, I'm sure that many know this.