Can anyone suggest something that will permanently stain keratin?

This is actually for keratin in the living animal; I want to mark the (light
colored) hooves of Merino sheep so I can track rate of hoof growth. But I
figured Histonetters would have some good ideas...what stains just won't
come off your fingernails!?

Thanks in advance,


Rosalind Dalefield BVSc PhD DABVT DABT
Senior Research Scientist, Toxicology
Plant Toxins Unit
CSIRO
5 Portarlington Rd
Private Bag 24
Geelong
VIC 3220
Australia

Phone 61 3 5227 5730
Fax     61 3 5227 5555
E