Greetings all,
     Last fall, I had a bout with robbing, not from one of my own hives, but
a feral colony a distance away.  What seemed to work the best was a
combination of tactics to stop it.  First, I reduced the entrances of the
hives down to the point where only a single bee could get in.  Next, I cut
several cedar branches and slightly hid the entrance.  Lastly, I sprayed a
mist of water onto the front of the hives.  This seemed to slow the problem
down a lot, and by the next day, it was over. It was not a pretty sight, and
there was a noticeable loss of bees in the affected hives.  Clearly,
prevention is much easier than stopping it once it starts!
Scott