Aren't you referring to "Mending Wall,"the poem by Robert Frost?
Frost expresses in these lines the "necessity" for barriers in spite of good will and even friendship. The fact that the two neighbours help each other maintain the wall between their properties graphically demonstrates this. Frost wonders why his proximity to his neighbour should be a potential menace of intrusion. Wouldn't they still be good neighbours if the wall were not there? Perhaps the answer is "Yes," but the wall concretizes their separation, their need for privacy and even exclusion. Rebuilding the wall together ironically honours this unspoken code of conduct. The age-old adage is indeed well put: 'Your liberty stops where another person's begins.'