Where is an example of how the Mossbachers are a part of the walls in "The Tortilla Curtain"?

The building of literal walls is not a hidden theme in the novel - much of the controversy from the start concerns the building of first a gate and then a wall for Arroyo Blanco, and the entire novel is based on the consequences of immigrants jumping the "wall" of the Mexico-U.S. border. The literal wall appears in several other ways as well. The coyotes must get over the Mossbachers' fence in order to grab their dogs, and they are able to do so with skill and cunning, similar to the ways in which Mexican immigrants overcome the wall at the border. The canyon wall is another important one, separating Cándido and América from the safety, comfort, and prosperity of the white Americans and their lives. However, the figurative wall is just as important and present in the novel, though much harder to see. A "wall" exists between the Mexicans and the white Americans restricting interactions between the two. Rarely in the novel does the reader see any conversation between people of the two races, and when it is seen it is usually forced and filled with hate and anger. From youth, Cándido has been taught to build a "wall" between himself and the rest of the world when things become difficult.

These walls serve two purposes: two keep things out as well as to keep things in, something that Delaney realizes when he hears the racist conversation of Jack Jardine, Jr. and is saddened to know that the new Arroyo Blanco wall will keep people like him in. They protect the ordered, regimented, white worlds from the wild and untamed people and forces that exist, but at the same time they trap inside the monotonous ideal, comfortable and coveted though it may be. The Arroyo Blanco wall does this, as does the wall around the Da Ros property. It encloses Kyra's dream home and dream life and protects it, and it is because of this that the breach of José Navidad and his companion is so frightening to Kyra. It was a breach of her walls and a breach of her privacy. Yet although it is Kyra's dream, what is enclosed is actually quite sad, a large, empty home marred by suicide. On a much higher level, the same frame of thought can be applied to the wall at the border. It keeps out the "wild" Mexicans that people fear, yet at the same time the cherished, longed-for life that it encloses is marred with greed, waste, and repression.