The Black Rhino per se is not extinct, only the Western subspecies. There is a way to preserve the ones that are left:
Give the locals exclusive rights over the rhinos: they can harvest the horns of dead rhinos and whatever else they want from it. That gives them an incentive to actively oppose poaching and to preserve the species and reduces the market value of the horns to poachers: as with marijuana, an outright ban just makes the horns more valuable, and adds to the incentive to poach.
Give the locals exclusive rights over the rhinos: they can harvest the horns of dead rhinos and whatever else they want from it. That gives them an incentive to actively oppose poaching and to preserve the species and reduces the market value of the horns to poachers: as with marijuana, an outright ban just makes the horns more valuable, and adds to the incentive to poach.