OK, time to play "Guess that metaphor!"
Gurov went without haste to Old Gontcharny Street and found the house. Just opposite the house stretched a long grey fence adorned with nails. […] "One would run away from a fence like that," thought Gurov, looking from the fence to the windows of the house and back again. […] He walked up and down, and loathed the grey fence more and more, and by now he thought irritably that Anna Sergeyevna had forgotten him, and was perhaps already amusing herself with some one else, and that that was very natural in a young woman who had nothing to look at from morning till night but that confounded fence. (3.16-9)
Anna is symbolically confined by the fence outside her husband's house, just as she is actually confined by her marriage. In fact, both she and Gurov feel trapped in their lives and are longing for an escape through each other. Even more significant in this passage here is the fact that Gurov is, perhaps for the first time, really seeing the world through Anna's eyes. He's understanding her perspective, which goes some way in breaking the boundaries that separate them from each other.