Story highlights Despite efforts to preserve South Africa's rhinos, a record number were killed last year

Rhino horn can fetch up to $5,550 an ounce on the black market in parts of Asia

Hoedspruit, South Africa (CNN) For the second night in a row, Mark Preston and his motley crew of anti-poaching rangers are waiting to spring a trap.

"We're hunting poachers all the time," Preston said. "If you just sit and wait for gunshots, all you get is carcasses."

Preston, a former metal worker in Johannesburg, says he needed a change when he left for the bush more than a decade ago. The job used to focus primarily on wildlife conservation. But now Preston and his men look more like paramilitary soldiers, complete with berets and semi-automatic guns.

To save South Africa's remaining rhinos, intelligence is everything.

"As far as I have been told, they're coming this way," he says, pointing down the road with his cigarette. "They're going to be chased this way and I am going to box them in."

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