Rhino farming (like farming of crocodiles, ostriches etc.) is an idea which I heard several times over decades. Several factors make it infeasible as a strategy for saving rhinos.
- Rhino horn grows very slowly,
- In every African country outside South Africa, a farm of rhinos would be invaded by poachers who would kill rhinos, so conveniently brought in one place, and probably murder the staff. Basically, crime/law enforcement issue.
- The problem of certification of legal horn and legal horn creating interest and increasing poaching for illegal horn, rather than reducing it. This might be theoretically solvable with very good enforcement in Arabian countries and South Asia, but most people belive it is not realistic now.