Montana is bear country.  Our Beekeeping Association and Fish and Wildlife
Department have worked up methods of keeping bears out of yards.  So far,
the only dependable method is an electric fence, but not any old fence.
Our beekeepers can get a solar charger from the State.  The fences are weed
zappers - they really pack a wallop.  Because our climate is dry in the
fall when the bears are down in the lowlands and hungry, a wire mesh is
laid flat on the soil in front of the fence to make a fool proof ground.
The bear has to stand on the mesh when he/she hits the fence.
 
This approach does work.  But the cheap fence chargers and poor grounds don't.
 
As per requeening by commercial operations (which is mainly what we have),
George Imrie has it right.  Our folks normally requeen in their stockpile
yards, right after taking the 1-2 story units off the truck.  And most do
find the old queen and pinch her, but a good crew can do several hundred
hives in a day.
 
As George said, they play the odds.  If they don't find her fast, they move
on to the next hive.  Some will come back later, other will just drop in
the new queen.  But, we have worked in commercial yards with 50-100 hives
and watched a 2-3 people inspect the entire yard in less time than the
average person with 2-3 hives in the back yard.  But they don't waste any
time or effort.
Jerry J. Bromenshenk
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http://www.umt.edu/biology/bees