This is a very interesting article about beehives used to keep out elephants:
African elephants are afraid of bees (they even have an alarm call for them), and scientists are now using that fear to help protect the crops of Kenyan farmers. In previous studies, a team of researchers showed that the behemoths rapidly leave areas where they hear the sound of buzzing bees. Now these same scientists have designed and tested a fence that incorporates beehives spaced 10 meters apart. The team installed 1700 meters of the fences along the boundaries of 17 farms in Northern Kenya that are often raided by wild elephants; another 1700 meters of the same farms were protected only by thorn tree fences. After two years, the beehive fences easily won the contest: only one bull elephant broke through this fence, while 31 elephants managed to crash the thorn fence, the scientists report in the current issue of The African Journal of Ecology. Beehive fences can thus be used to help limit the number of human-elephant conflicts, a growing problem as the human population in Africa increases, and farmers and elephants compete for land and water resources, the researchers say.