What solution did u go with in the end and did it work?
Incidentally, I sprayed some lambs over a week ago using a can from the Net-tex goodie bag and another ritchey one that I already had. The Ritchey spray mark was pretty much gone after a couple of days, the net-tex one is still going strong!!!! Just a shame they sent me red and blue, I don't think blue will show up on black, but I might give it a whirl.
Thanks Net-Tex/Rumenco