For the last several years, dye and poison have been utilized in the fight to protect rhinos from poaching. The dye has a threefold benefit: it shows up in airport xray, even when ground, it is brightly colored so consumers, etc know the horn is contaminated, and it will make the end consumer of the horn sick. Scientific American published a well written article on the subject in 2013. Follow the link below for more reading of this encouraging news.