A recent commenter referred to “the nation within.” For those of you who don’t know the Chet and Bernie novels, that’s the source he had in mind. (Chet, the narrator, is a dog – but not a talking one!) The first mention is in Chapter 23 of Dog On It, the first book in the series (which can be read in any order!):

The biker opened the door and we entered the building. We were in a small room with a counter, a woman behind it, and lots more smells, all from members of my nation. That was one of Bernie’s ideas – we were a nation inside of a nation.

The woman looked up. Her smile faded quickly when she saw the biker. “Help you?” she said.