There are multiple figures of speech (or literary/poetic devices) used in Robert Frost's poem "Mending Walls."
Alliteration- Alliteration is the repetition of a consonant sound within a line of poetry. For example, in the tongue-twister "Peter Piper picked a peck of pickled peppers," the repetitive sound of the "p" exemplifies alliteration. In the initial line of the poem, alliteration is found.
Something there is that doesn't love a wall.
In this line, the "t," or "th," sound in "there" and "that" is repeated.
Assonance- Assonance is the repetition of a vowel sound within a line of poetry. In the children's game "I Spy," the vowel sound "i" is repeated. Assonance can be found in the third line of the poem.
And spills the upper boulders in the sun.
In this line, the vowel sound "u" in "upper" and "sun" is repeated.
Metaphor- A metaphor is the comparison of two or more things which are typically different. An example of a metaphor is "My life is a roller coaster." Here, the speaker's life is compared to a roller coaster (meaning his or her life is full of ups and downs.) An example of a metaphor can be found in line twenty-four of the poem.
He is all pine and I am apple orchard.
Here, the speaker is comparing his or her neighbor to a pine tree and himself, or herself, to an apple orchard.
Personification- Personification is the giving of human characteristics or traits to non-human/ non-living things. For example, "the sun smiles" is an example of personification given the sun cannot smile, but humans can. Personification can be found in lines twenty-seven and forty-six.
"Good fences make good neighbors."
Here, fences are given the ability to be a good neighbor. Given that only humans can make good neighbors, this shows the personification of the fence.