The Dinokeng Game Reserve in South Africa has a thriving rhino population, but their exact numbers and the details of the security operation that keeps them safe from poaching are closely guarded secrets. They are protocols that reserves with rhinos follow to safeguard against poachers who still kill on average one rhino a day in South Africa. South Africa has the largest populations of both black and southern white rhinos of any country and sees itself as the custodian of the animals' future. As conservationists mark World Rhino Day on Monday, the AP reports that South Africa remains in a constant and costly battle against poaching nearly 30 years after black rhinos were declared critically endangered, and more than a half-century since southern white rhinos were on the brink of extinction. A look: