Several rhinoceros species are on the verge of extinction. What can be done to save them?

I think that synthetic rhino horn could work if it is much cheaper than natural rhino horn — and similar enough to fool purchasers. Anyone who claimed to sell "natural rhino horn" would probably cheat.

In the long term, even if we eliminate the threat of poaching, not much wildlife will remain if humans convert all wild areas into farms and cities. We must curb human population growth to enable most wild species to survive.