I won't attempt to involve myself in the ethics of pets on boats, but I do have a few words about training a dog to produce a product on deck. At this time our eight year old Schipperke lives aboard and fulltime cruises with us. If we call out the command word, "Lido", he runs to the stern and where he is expected to perform. We accomplished this by restricting him to this area for periods of time when he was a puppy and rewarding his performance. I have heard of people having success with designated pads and placing dog urine samples at a desired location, but we were successful with patience, repetition and reward.
...'take care and joy, Aythya crew