Mike I do not know what kind of leather your guard is but some leather does not tool well. Veg tan is the only leather that can take water and be cased to be tooled or formed. Also once a project is finished it is usally oil and sealed which makes tooling next to inpossible. If it where done I dont think the results would not be very good. The easiest thing would be to find a laser ingraver in your area and have them laser ingrave the leather. I have used laser ingraving in the past for complicated patterns like a logo and it is sharp! Your results will probably be the best for the application.
Scott