Many have argued that the entire poem is a metaphor, though Robert Frost cautioned against reinterpretation by those who read the poem's wall or fence as the Berlin Wall and the poem as standing for the Cold War.
The neighbor's motto is a paradox: if the neighbors were really good neighbors, they would not really need a fence. The narrator teasingly points to this contradiction.
There is only one simile, using like in comparing the neighbor to a savage:
like an old-stone savage armed.
Within the personification of the trees, one finds a metaphor for inappropriate border-crossing, for the trees can only figuratively move or eat.
My apple trees will never get across
And eat the cones under his pines....
The neighbor's negative attitude is metaphorically compared to darkness:
He moves in darkness as it seems to me,
Not of woods only and the shade of trees.
Frost uses alliteration sparingly; in contrast, assonance...
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