On October 26, 2006, President George W. Bush signed the Secure Fence Act of 2006 into law. However, the U.S. Department of Homeland Security (DHS) successfully argued to Congress "that different border terrains required different types of fencing, that a one-size-fits-all approach across the entire border didn't make sense." An amendment introduced by Senator Kay Bailey Hutchison, Republican of Texas, was passed, amending the law to read: "nothing in this paragraph shall require the Secretary of Homeland Security to install fencing, physical barriers, roads, lighting, cameras, and sensors in a particular location along an international border of the United States, if the Secretary determines that the use or placement of such resources is not the most appropriate means to achieve and maintain operational control over the international border at such location." (PolitiFact). Obviously, DHS had, since 2007, begun to shift its focus to erecting a 'virtual fence' along the 2,000-mile border, using sensors, cameras and other high-tech equipment to prevent illegal crossings. Nevertheless, by May 2011, DHS reported completing 649 miles of fencing (99.5% of the 652 miles planned.)

Ignoring experts, Trump proposed a wall which he said would consist of 2,000 miles "of hardened concrete, and ... rebar, and steel" across the entire southern border.

Amy Patrick, structural engineer, professor of structural analysis and design at the University of Houston and court-recognized expert on walls, stated in an article: “Structurally and civil engineering-wise, the border wall is not a feasible project. Trump did not hire engineers to design the [wall.] He solicited bids from contractors, not engineers. This means it’s not been designed by professionals. It’s a disaster of numerous types waiting to happen.” Among the problems Patrick listed are these:

There is no provision for drainage of flash flood waters. Any holes would dramatically impact the effect of flooding and impede our ability to control it.

It is damaging ecologically. For all other projects, it is necessary to do an Environmental Site Assessment, which is arduous. They’re either planning to circumvent all this, or they haven’t accounted for it yet, because that’s part of the design process, and this wall hasn’t been designed.

The prototypes they came up with are nearly impossible to build, or don’t actually do the job. (“Writing on the Wall: Report Suggests Border Project Is Off-Track and Over Budget” - Engineering.com)

Unless they want to build a barrier down the center of the Rio Grande river, the government will have to obtain land from owners by the right of eminent domain. Legal challenges and expenses on these inevitable challenges will take $ Millions and years to resolve in the courts.

Another concern is the temptation for awarding no-bid contracts to firms who have connections to political figures both state and federal for vast amounts of money who would personally profit greatly from additional construction. One can only wonder if Trump would have doubled the fees for his Mar-A-Lago guests had he not been in office, and what financial ties the President and politicians have with potential bidding contractors.

"The estimates provided for the cost are arrived at unreasonably – reference the two-year-old estimate that everyone is citing.” (fronterasdesk.org “Who Would Profit from the Trump Wall?” by Phil Roseberg, Paul Gait, Jeremy Redenius, PhD, and Jonas Oxgaard, PhD.)

“It’s going to be higher than $50 Billion,” stated Patrick. “The contractors will hit the government with near constant change orders. 'Cost overrun' will be the name of the game. It will not be completed in Trump’s lifetime. So you’d end up with a revolving door of contractors making a giant, uncoordinated muddle of things, and it’d generally be a mess. Good money after bad. The GAO agrees with me. I could, right now, purchase a 32 foot extension ladder and weld a cheap custom saddle for the top of the proposed wall so that I can get over it. I don’t know who they talked to about the wall design and its efficacy, but it sure as heck wasn’t anybody with any engineering imagination.”