yard dog
n.— «The yard dogs—prison vernacular for guards—were already baying. Someone had issued a Signal 3, a man-down alert, and guards descended from all directions.» —“Gang life at prison on trial in murder case” by Ted Wendling Plain Dealer (Cleveland, Ohio) Feb. 27, 2005. (source: Double-Tongued Dictionary)
Further reading
What kind of book do people ask for most often in prison? Romance novels? No. The Bible? No. The most requested books by far are … dictionaries! A number of volunteer organizations gather and distribute used dictionaries to help inmates with...
What if, instead of being an inanimate object, a dictionary were alive? That’s the idea behind a lavishly illustrated new children’s book called The Dictionary Story (Bookshop|Amazon) by Oliver Jeffers and Sam Winston. This is part of a...