Instead of condemning the land around the border and putting up a steel barrier; create an economic zone from sea to shining sea that will make the area an international destination, a source of revenue, a safe zone where cartels will be cleared out by a bilateral police force, and bring prosperity to the southwest United States and northwest Mexico.
The US-Mexico Canal will "trump" the Panama Canal and the proposed ones in Nicaragua and southern Mexico by being the biggest in the world. The border is approximately 1,954 miles. The Panama Canal is only 40 miles long. The Suez Canal is 120 miles long.
Assume over 1,500 ships passing through and 2.8 billion dollars in revenue annually and it is certainly a better alternative to just putting up a fence. It could be constructed like the transcontinental railroad, with teams starting at each terminus and meeting in the middle. Make it wide enough now to fit any planned larger commercial tankers and warships and it could be prosperous for 300 years.
Joshua Gelertner made a similar suggestion in the Weekly Standard in February of 2017: https://www.weeklystandard.com/joshua-gelernter/instead-of-a-wall-build-a-canal
Our government can begin by negotiating to acquire one and a half miles of land north of the border along the entire route. The Mexican government should do the same. This will allow for the widest canal possible and include retail, commercial, entertainment and residential sites along the route.
The construction contracts can be negotiated internationally with preference being given to US and Mexican companies on the respective sides. One great source of labor can be veterans. Prefabricated dormitories can be set up at the work sites and disassembled and relocated as work progresses.
Security will be an important factor during the entire process, and removal of the drug cartels as mentioned previously will create a welcome respite for the residents living near the sites on both sides.
Side benefits of the canal would also include climate change due to the influx of water into the Sonoran Desert. The Pacific Ocean at the western terminus is approximately 63 degrees Fahrenheit. The Gulf of Mexico near Brownsville is around 74 degrees Fahrenheit. The influx of an average temperature of 70 degrees along a 2,000 mile route, half a mile wide, plus evaporative effects will have a non-insignificant impact on global warming.
Let's at least explore the concept....
Solve Floods and Droughts in One Wave!
The Southwest United States has been suffering from an epic drought. Lakes are drying up. Wildfires are spreading. The quality of life is impacted.
The Southeast United States is constantly suffering from 100 year floods.
The solution is of course move some water from where there is too much, to where there isn't enough. How? Build an aqueduct from the Mississippi River to the Colorado River.