SECURITY: Attack of the Killer Shrub

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Scientists call it trifoliate orange. Barrier Concepts Inc. uses the brand name Living Fence. Most appropriate, perhaps, is its more common nickname "P.T.," which stands for "pain and terror."

That is what intruders experience if they try to penetrate one of the newest and most unusual security devices on the market: rows of P.T. bushes used as fences. Amid the innocuous-looking white flowers and glossy green leaves are 4-in. razor-sharp thorns that make the bushes nearly impossible to climb over and are strong enough to stop a speeding jeep. P.T. plants grow naturally in the hills of East Tennessee, sometimes reaching a height of 20 ft., and have long been used by local farmers to protect livestock. Now Barrier Concepts, an Oak Ridge, Tenn., firm, is selling the bushes to such security-minded customers as the CIA, the Secret Service and the military. The Marine Corps Air Station in Cherry Point, N.C., bought 32,000 of the bushes to encircle ammunition depots, fuel bunkers and runways. "You'd need a chain saw to get through them if you could get close enough," observes a Cherry Point security officer.

A Living Fence costs $3 a foot, in contrast to $42 a foot for a chain link fence. Except for an occasional pruning (which must be done carefully), P.T. plants require virtually no maintenance. They take five years to reach effective size, but Barrier Concepts says the bushes last up to 35 years, three times as long as most metal fences. The firm hopes to sell its product to private citizens, perhaps by pushing the idea that Living Fences make the best neighbors.