What about a combination barbed wire/electric fence (alternating
strands).  Have you tried filing a report with the police?  It lets them
know that something is going on, and if you do catch the person doing it
you should be able to do something about it.  As for liability... I'm
sure the idiot pushing over your hives could get away with suing you if
he get's stung...  This is what the world has come to I'm afraid...
Maybe it would help to put up some signs warning of the hot wire, and the
dangers (however remote) of being stung.
 
This is advice coming from a non-beekeeper, but I do keep wildfowl and
deer, so some of these techniques are drawn from that experience.  Hope
this helps...
 
Stacy L. Spitz
) 1998 Stonegate Meadows
http://www.geocities.com/Heartland/Ranch/1393
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