Robert Frost 
North of Boston 

SOMETHING there is that doesn't love a wall, That sends the frozen-ground-swell under it, And spills the upper boulders in the sun; And makes gaps even two can pass abreast. The work of hunters is another thing: I have come after them and made repair Where they have left not one stone on a stone, But they would have the rabbit out of hiding, To please the yelping dogs. The gaps I mean, No one has seen them made or heard them made, But at spring mending-time we find them there.