By Victoria Gill
Science and nature reporter, BBC News
Raoul du Toit is director of the Lowveld Rhino Trust in Zimbabwe
Raoul du Toit, a Zimbabwe-based conservationist who has taken a very direct approach to saving Africa's Critically Endangered black rhino, has been selected as one of the six winners of this year's Goldman Environmental Prize.
The prize, founded by American philanthropist Richard Goldman, is the world's largest award for grassroots environmentalists.
One recipient from each of the world's six inhabited continents will receive the $150,000 (£92,000) prize.
Mr du Toit's fellow recipients include a biologist who initiated a local movement to stop industrial pollution flowing into an Indonesian river that provides water to three million people, and an activist who has fought to protect a remote island off Russia's far east from being damaged by an oil development project.
Raoul du Toit founded the Lowveld Rhino Conservancy Project in 1990, whilst he was working with the World Wildlife Foundation.
He is now director of the Lowveld Rhino Trust, and his work over more than two decades has saved Zimbabwe's black rhino population from being permanently decimated by poaching.
"In the late 1980s, Zimbabwe had Africa's largest black rhino population - about 1,500 animals," he explained.
"But cross-border poaching by Zambian gangs devastated the populations and by 1992 rhino numbers had fallen to under 600.
"We wanted to put these rhinos somewhere safer."
Throughout the project, he and his colleagues moved black and white rhinos away from the border into a range of conservancies in the Lowveld region.
Since the area was home to many large cattle ranches, he worked with the ranchers - in particular in helping them install perimeter fencing, to allow them to farm alongside the vast open plains that the rhinos need to range.
This was almost an immediate success; the thriving wildlife tourism industry meant that protecting rhinos was profitable for the private sector.
Breeding projects were set up and the rhino population recovered dramatically.
But in 2000, the private sector strength of these areas became their weakness.
Chaos and opportunity
Robert Mugabe's government turned ranching operations in Zimbabwe upside down.
"With the draconian land reform policies, the private ranching areas were subject to nationalisation - and subsistence farming expanded into the conservancies," Mr du Toit recalled.
"With the economic decline and political insecurity, the rhinos weren't able to pay their way any more."
Though many conservation projects collapsed as professionals left the country, Mr du Toit has continued his work.
"Politically, we are in a mess right now and we need to get out of it, but in times of chaos there's also some opportunity," he told BBC News.
Rhino poaching was exacerbated by Zimbabwe's political instability
"Because we don't have a country that's rigidly governed - that's set its own development goals - we can set out our own path and make alliances with people who want to plan for the future of Zimbabwe."
A reduction in law enforcement, though, has coincided with an increase in poaching in the formerly well-protected area.
The animals are slaughtered to supply the the illegal trade in rhino horn, which is a rare and prized commodity fetching high prices in Asia.
Mr du Toit's solution is to work with local communities in Zimbabwe, to make rhino conservation a self-sustaining business once again.
"We want to buy rhinos from the commercial operations and give them to local communities," he explained.
He envisions the money generated - from, for example, international development funds and from wildlife tourism - going into a trust fund that would pay a sort of dividend for these locally-owned rhinos.
"So we would be able to pay people every time a rhino is born in their community."
The Lowveld conservancies are now home to more than 400 black rhinos, 7% of the entire global population.
And Mr du Toit is optimistic about the future.
He says it is "a completely inaccurate cliché" to portray rhinos as dinosaurs that are due for extinction.
Mr du Toit concluded: "They are biologically capable of thriving and contributing to wildlife-based tourism to the extent that they definitely have a future in Africa if poaching can be controlled."
The Goldman Prize is in its 22nd year. The six winners will be awarded the prize at a ceremony at the San Francisco Opera House in the US on Monday.
Francisco Pineda (r) risks his life to protect El Salvador's water resources
This year's other winners are:
• Francisco Pineda, from El Salvador, led a citizens' movement that stopped a gold mine from destroying the country's water resources. He now lives under constant threat of assassination and has 24-hour police protection.
• Dmitry Lisitsyn, from Russia, who has fought to protect the threatened ecosystem of Sakhalin Island in Russia's far east from being damaged by a large petroleum development project.
• Ursula Sladek, from Germany, created her country's first cooperatively-owned renewable power company.
• Prigi Arisandi, from Indonesia, initiated a local movement to stop industrial pollution from flowing into a river that provides water to three million people.
• Hilton Kelley, from the US, has fought for poor communities affected by pollution from petrochemical and hazardous waste facilities on the Gulf coast of Texas.
Hilton Kelley fights for poor communities affected by industrial pollution