"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."
Preston scrapes a diagram in the dirt with his boot to go over tactics. They've got a tip that a group of poachers is heading into this section of private game reserves bordering on South Africa's giant Kruger National Park.
"I want aggression, aggression," says Preston, taping on his sidearm as he speaks.
But despite the foot patrols, CCTV cameras, and special task teams, this area alone lost four rhinos in one night last week.
Conservationists and anti-poaching groups say it is part of a disturbing new trend.
Poaching operations used to be based in Mozambique and launched into South Africa from the east.
Now, they say most poaching operations here are increasingly launched from the western side of the reserves, from South Africa's heartland.
In South Africa's iconic Kruger National Park, 750 rhinos have been poached this year alone. Last year 1,215 were slaughtered across the country -- that's one every eight hours, according to Save the Rhino.
Poachers normally work in small groups, with a heavy caliber weapon to shoot the rhino, and small arms to protect against rangers like Preston.
For many, the prize is worth the risk. Rhino horn fetches more than its weight in gold in Vietnam and China, driven by an insatiable demand where it's prized as a sign of wealth and mistakenly believed to have medicinal properties.
Rhino horn is made of keratin, the same protein found in the human fingernail. Still, it fetches as much as $5,550 an ounce on the black market.
Conservationist have tried everything to stop the slaughter: They've relocated rhinos from Kruger to fenced-in private parks; they've protectively removed the rhino's horns; they've poisoned and dyed the horns.
None of it seems to have worked, however, and private and national reserves are now turning to military tactics.
Groups like Protrack, a paramilitary-style anti-poaching group, are putting new recruits through a punishing six-week boot camp to rush them into combat against the poachers.
Just five years ago, rangers trained on conservation and tourism. Now they're also learning how to handle semi-automatic weapons and court cases.
Rangers train for months to read signs of the bush -- and anything that seems out of the ordinary needs to be called in. Litter, footprints, broken branches: any of it could signal the presence of poachers nearby.
But this bush war approach doesn't seem to be working either.
"We have to get feet on the ground with guns," said Vincent Barkas, the owner of Protrack. "Unfortunately, the feet on the ground with a gun that kills a poacher is the wrong way forward. We are causing more resentment towards our wildlife and towards conservation as a whole than we are doing any good."
Barkas says that in an area wracked by unemployment and historical inequality, there is often not much love lost for the private reserves here that shelter nearly a fifth of the country's rhino population.
Preston and his team have been waiting for hours in darkness by the side of the road for their intelligence to come through.
But they admit that often the informers are playing a double game because the poachers can pay them more.
The phone finally rings. The operation is called off.
"There are times that the information is good and you can knock the guys, but that doesn't happen every day," says Preston. "You just have to keep at it."