I have 2 black labs and am bitten currently in researching mode. They're great dogs and i truly believe i can train them to do just about anything. I'd be very interested to see how other people do it. I'd hate to leave my water dogs behind to go play in the water.
we have had two dogs (small) that were both trained to use puppy pads we got at Pet Smart. we rinse them out and use them repeatedly. The current dog will run around and smell the grass when we are ashore but will usually wait until she gets back on the boat to do her business.
I have an 8 year old toy poodle...she uses those PeePads. I'm usually only out for 2-3 days at most and anchor up by an island so we can dingy over tot he island and she can run around...peee and poo to her hearts delight.