I think a case can be made for the value of a fence between neighbors, in spite of all the reasons Frost presents to the contrary in "Mending Wall." Even he concedes that such a fence or wall would make sense if there were cows. I lived next to a cattle ranch in Missouri for about a year, and the rancher's cows would frequently come visit me. As a city girl, I found this terrifying and would have appreciated a fence. There are other circumstances in which fencing would improve the relationship between neighbors. For example, if I had no children and my neighbor had children who kept straying onto my property, perhaps littering or doing some mischief, a firm boundary such as a fence or a wall would help us to maintain a more pleasant relationship. If I had a dog that I let out on its own on my property and it kept straying onto my neighbor's property, my neighbor would probably not be very happy about that, and a wall or a fence would get us on better terms. In cities, which sometimes have mixed-use zoning with residential and commercial uses in close proximity to one another, fences and walls can save a great deal of trouble between residents and businesses that find themselves to be neighbors. So, while I agree with Frost that his neighbor's saying is not particularly apropos in the setting of the poem, I can see a need for fences and walls.