[ Clancy / Patriot Games ]
First published in 1987, this is one of the series of "Jack Ryan" novels by Clancy; it has one incidental mention of Newfoundlands, at the point in the story when Jack Ryan, having just brought home a Labrador Retriever puppy, is talking about the dog with his wife:
"I was going to get a Newfoundland, but they're just too big — one-fifty." Jack didn't say that his first wish had been to get a dog big and tough enough to tear the head off anyone who came close to his daughter, but that his common sense had prevented him." (364 in the 1988 Berkley paperback edition)
Not, of course, that a Newf would be the breed of choice for someone looking for a protection dog.... Doberman Pinscher, anyone?