But Frost didn't invent that phrase. I hadn't read the poem since school, so I didn't consider it before. But looking at it again now I notice that the phrase is presented in an ironic way. So I turned to the power of the internet and found that, indeed, "good fences make good neighbors" predates "The Mending Wall" by about 30 years.

https://books.google.com/books?id=zAgTAAAAYAAJ&dq=%22good%20...