In constructing more than 600 miles of border walls that slice through all manner of landscape, the Department of Homeland Security (DHS) has used a wide range of designs. In some cases, these appear to have been developed on the spot, with little or no forethought, while others were developed at a "fence lab," where the wall designs were subjected to potential abuse by Border Patrol agents to determine how long it will take a prospective crosser to climb or cut them. In general, the Border Patrol states that all walls take "minutes" to breach.

Border walls fall into two general categories, which the Border Patrol refers to as "pedestrian fencing" and "vehicle barriers." Pedestrian fences are meant to stop crossers on foot, and are 15 to 18 feet tall, while vehicle barriers are only intended to stop vehicles.

"Pedestrian Fence" Designs

The earliest "pedestrian fence" designs were erected in California and Arizona, and consisted of helicopter landing mats left over from the Vietnam War and other scrap metal crudely welded together.

When these failed to achieve their goal of preventing undocumented immigrants from entering the United States, Boeing developed the "triple fence." Essentially, this involved adding a second steel mesh wall north of the scrap metal wall, and constructing a road in between the two.

The first "triple fence" was touted as more humane than walls in Berlin or Israel because of its lack of concertina wire and concrete, but in 2008 concertina wire was added to the top of the wall in San Diego.

As DHS increased the pace of border wall construction following passage of the Secure Fence Act, the supply of scrap steel began to run low. They then began using prefabricated steel mesh panels.

The border walls made of steel panels and steel mesh were subject to frequent breaches, as those wishing to get past them cut through with portable torches and saws. In an attempt to construct border walls that would not be so easily cut, the "bollard fence" was developed. These consisted of pipes filled with concrete, and spaced too close together for a person to squeeze through.

In the rugged mountains of California and Arizona, a border wall design using prefabricated steel bollards has been employed.

In the sand dunes between Yuma, Arizona and Calexico, California, there is no solid ground beneath the border line. The PV-4 "floating fence" design is intended to place the border wall on top of the shifting dunes. When sand builds up against the wall and threatens to bury it, work crews use a machine to lift the wall sections and reposition them on top of the dunes.

In South Texas the boundary between the United States and Mexico is in the middle of the Rio Grande. The treaty that established the international boundary forbids either nation from erecting any structure in the river's floodplain that might exacerbate flooding on the other side or alter the course of the river. A wall built between the levee and the river might deflect flood waters south, causing the river to settle into a new channel and changing the location of the border. Levees on both sides are evenly matched, and constructed in consultation with the bi-national International Boundary Water Commission (IBWC). For this reason, border walls in south Texas must either be built on, in, or to the north of the IBWC levees, which are in some places as much as two miles north of the Rio Grande.

In Hidalgo County, Texas, the river side of the flood control levee was carved away, and the formerly sloping earth was replaced with a sheer concrete slab. This was topped off with steel posts.

The levee-border wall combination cost upwards of $12 million per mile, so in other parts of South Texas different designs were used. One was the P-3B-15 "floating fence", in which steel posts were set into prefabricated concrete "jersey barriers," which are similar to those used to divide a highway. These are placed either on top of the IBWC levee or to the north of it.

Two other designs have been used to construct border walls in South Texas. One is a modified steel bollard design, erected north of the IBWC flood control levees.

In Brownsville, Texas, DHS has used a "pedestrian fence" design that uses prefabricated panels made of thinner steel rods welded into a steel frame similar to that of the mesh panels used in Arizona and California.

Vehicle Barriers

In remote parts of Arizona and New Mexico, vehicle barriers have been erected. There are a number of modifications of two main designs, referred to as bollard and Normandy barriers.