I don't see any outstanding flaws with the grammar. So I would say it is correctly written.
Well, I think, the main point that makes the difference between "Mending Wall" and “The Purple Cow” is actually demonstrated by the rhyme. Just read each poem one more time and feel that one of them is readed easily, words matched with each other like a song's lyrics so that you can smoothly go on reading whereas "Mending Wall" is made with structure of blank verse that emphasises every line and makes reader feel it deeply.
