Been to the mouth of the Wye myself. What a place!
Dave hit the nail on the head when he mentioned "smell". Dog's are scent oriented as I'm sure you have noticed. Do not clean that piece of grassy thingy too well as you want her to be able to smell it again so she repeats her performance. It only takes one dog to start a pissing contest! This is how they get a dog to pee on cue on TV is make sure it smells another dog's urine in that spot. I'm not sure how well human pee would work but might be worth a try in small doses.
Still that is progress. I'm glad you seem to have the patience to deal with your rescue dog. If you keep up the good work you might very well have a boat dog on your hands.
Yeah, she's doing great. She gets excited about being on the boat, and has figured out when the boat starts bouncing or rolling to just hunker down. The only really big hurdle is making sure she can go when she needs to go. She has an iron bladder--seriously she can wait. But we don't want her to. So progress is progress.
All we did with the Pup Head was dunk it. No soap or anything. Fingers crossed for next time...