The use of rhino horn to treat impotence is a perfect example of the "pseudo-homeopathy" (belief that like cures like) found in traditional healing... That big hard horn is intuitively seen as a remedy for failure to get an erection. For men whose impotence is partly psychological, of course, a strong belief in the power of rhino horn might indeed be effective. This no doubt is the reason why the demand is so great and persistent.
In terms of debunking this deceptive, rhino-exterminating belief, health education clarifying the lack of any physiological/medicinal effect of rhino horn (beyond that of deception) should perhaps be tied to awareness-raising about the "pseudo-homeopathy" (or placebo effect) of countless forms of "magical" or traditional healing in many countries.
The power of suggestion does of course have an important place in healing - especially in traditional medicine. In their preparation, community health workers need to learn - and help their people to learn - to recognize the strengths and weaknesses of both "modern" and traditional medicine.