well now, I got a bottle free with a muddy marvel starter pack I ordered off t'internet.
We sprayed it on their legs, manes and tails. I'm not sure if it lasts 7 days, because we were washing the horses' legs each night we thought "ah better spray some more on" The mud does SEEM to come off easier when you hose or brush their legs. It's also pretty reasonably priced, I'm going to buy some more.