'Unbreakable' fence-protection device to fight rhino poaching

An innovative device that could reduce fence-protection cost to a fraction of what is required for current electrical fences could be used in South Africa to help fight poaching of critically endangered rhinos.

The device developed by South African engineer Ernst Pretorius, dubbed the fence-sitter, uses two acoustic sensors to monitor tampering on the fences up to an 800m distance.

The inventor, who was one of four runner-ups in the inaugural Africa Prize for Engineering Innovation run by the Royal Academy of Engineering, has been recently approached by managers of South Africa’s Kruger National Park to demonstrate the potential of the device to fight poaching.

“The device combines two acoustic sensors in one unit,” Pretorius explained. “One sensor measures ambient sound and the other acoustic sensor measures the ambient sound together with the sound on the fence. If you measure the difference between the two values, all the ambient sound is cancelled out, and you can detect intrusions on very long distances.”

Pretorius, who was prompted to look into the technology after witnessing the struggles of his farmer friend with cattle thieves, believes the fence-sitter is virtually unbreakable.

“One unit would be placed on the top of each fence post,” Pretorius said. “That means that to take one of the units out, you would have to climb on the post first and that would already raise alarm. There is a lot of redundancy in the system. You would have to take a couple of those units out at the same time to actually break the communication link.”

Currently existing electrical or optical-fibre based systems can, on the contrary, be easily bypassed by simply cutting the fibre or the electrical wire.

Pretorius argues his system would also come considerably cheaper.

“For about ten kilometres of fence, if your wiring posts are situated 200 metres apart, it would cost you something like 330,000 rands (£17,230),” said the engineer. “For the same ten km of fence, if you install a brand new electric fence with all the labour, material and things that go into it, it costs you something like 1.2 million rand. An optical fibre system would come even more expensive - about 2 million rand for 10km.”

The patented system could find many applications, protecting borders between countries or game reserves against unauthorised access.

The device raised interest of managers of South Africa’s Kruger National Park, who are currently in the middle of a desperate war against poachers. In 2014, more than 1,000 rhinos were slaughtered in the park by criminals looking to sell their horns in the black market – a big blow for the shrinking rhino population.

“We want to run trials with the fence-sitter in the Kruger Park this summer,” said Pretorius. “If it proves itself, they will probably give me about 40km of fence around the rhino sanctuary to protect. Eventually, we would like to cover an even larger area.”

Pretorius, clearly passionate about animal welfare envisions his sensors could in the future work in conjunction with drones that are already being trialled in the park to fight poachers. The units could effectively relay signals from the drones to data control centres to help dispatch help if intruders are detected.

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