Recently someone told me the term ‘salty dog’ refers to the practice of early maritime sailors taking dogs aboard ships as mascots because dogs could smell land before the sailors could see it, and would alert them when they were approaching a land mass so they wouldn’t sail past it in the dark. I had no idea if the statement was true or false, so I looked it up. ‘Salty dog’ is indeed a nautical term, but refers to a sailor who has spent extended periods of time at sea; however, there was an early practice of rubbing salt through a dog’s coat as an archaic practice to repel fleas. In theory, it probably worked because the dog, no doubt, died from sodium poisoning.
This does raise an interesting question. There is an Blues song, ‘Salty Dog Blues’, and the first line is, ‘Let me be your salty dog, or I don’t wanna be your man at all.’ What do you suppose that means?