Hyphens, En Dashes, Em Dashes

Q. Dear wise and knowledgeable CMOS person, a fellow writer and editor and I can’t agree. She insists that “well-trained dog” shouldn’t have a hyphen. I think it must have that hyphen. We were both pretty tired when this cropped up, so we ended up barking a bit at each other. We’d like to resolve this bone of contention by appealing to you, whom we both respect and trust. Whatever you say, we’ll abide by.

A. If the dog is well trained (no hyphen), it is a well-trained dog. Please have a long look at our hyphenation table at CMOS 7.85. (Just one reason we’re top dog.)