We in Bisbee live about 5 to 10 miles from the "wall," built around popular crossing points and towns years ago (about 20) to slow down uncontrolled immigration. A contingent of Marines were the first to start construction. Back then, we thought the idea was crazy because we all knew something about the long stretch of the U.S.-Mexico border, including Texas, New Mexico, Arizona, and California.
I am originally from Texas (San Antonio) and have visited border towns since high school. When I joined the Army in 1956, I went through basic training in El Paso, at Fort Bliss. We were allowed one weekend of leave which most of spent in Juarez, and even then I was amazed at seeing the number of people running across the Rio Grande (usually a mere stream) from Juarez, Mexico to El Paso under the nose of a watching Border Patrol and U.S. Customs officials.
Moreover, many from Mexico and who work and live in El Paso during the week, return at night or on the weekends to their family homes in Juarez. That scenario likely works with "Ambos" or both sides of the border. In my experience, Mexicans are hard-working and family oriented.
We often have driven New Mexico 9, or the 'back way' from Rodeo, New Mexico and following New Mexico's border with Mexico for well over 150 miles and on to El Paso. The border (and the wall) would have to follow the Rio Grande, past Presidio, Texas and then down the Texas-Mexico border, to the tip of Texas, at Brownsville. This is a huge stretch of country and the land is pretty unforgiving for those without water or food. It is mostly desert in our part of Arizona and along New Mexico's border. And that's not even considering the border of Mexico and California.
I am including an article by a structural engineer explaining just how difficult and expensive the wall would cost. The wall would decrease trade for towns on either side of the border and would be very costly to maintain. In my view this kind of barrier would attract people like the drug cartels with the money and means to breach the wall and that's not good.
Also, anyone familiar with the Gadsden Purchase will know how much of the U.S. formerly belonged to Mexico, and we "got" it after the U.S.-Mexican War, a war that a lot of U.S. officers fought in and later became Civil War generals on both sides (Grant and Sherman, and Lee). It is a rather sordid part of our history with Mexico, and Mexico's history is not so wonderful either.