The border between Mexico and the United States runs for almost 2,000 miles from the Pacific Ocean to the Gulf of Mexico. Most of that border is delimited by a simple barbed-wire fence (easily cut or trampled down) or by nothing at all. In the late 1990s and early 2000s there occurred a huge increase in the number of illegal immigrants from south of the border. Thus, in 2005, an estimated 1.7 million people tried to enter the United States illegally and more than 1 million succeeded. In 2006 Congress responded with the Secure Fence Act. This led to the construction of about 700 miles of razor-wire-capped concrete walls in places where the border adjoined dense urban areas. Such areas allowed illegal immigrants to quickly disappear, while wilder, more remote areas provided a sort of back-stop area in which it was more difficult to disappear. In these areas the Border Patrol uses drones, motion sensors, and vehicle patrols.
How well do these methods work? Either pretty well or not well at all. On the one hand, the success rate at entering the United States has fallen from 64 percent in 2005 to 46 percent in 2015; the total number entering the United States has collapsed from more than 1 million a year to an estimated 170,000. On the other hand, an average of 465 illegal immigrants per day succeed in entering the United States. The walls merely divert illegal immigrants around the walls and into other channels. Moreover, the 46 percent success rate suggests that only about 350,000 people try to enter the United States. This, in turn suggests that either the “push” factor driving Mexicans into the United States or the “pull” factor attracting Mexicans to the United States have declined. Certainly, the “push” factor from Mexico has declined. First, Mexican birth-rates have been dropping from 7 children per woman in the 1960s to 2.2 children per woman today. Second, in spite of the horrific drug war underway in Mexico, the economy is doing pretty well. So, there are fewer “surplus” Mexicans with less of a motive to leave. Third, most of the captured illegals are actually people in flight from the murderous violence plaguing Central American countries. Also, the stagnant American economy since the financial crisis has exerted much less demand for cheap foreign labor. However, should either the “push” or “pull” factors be heightened, then it seems reasonable to conclude that illegal immigration would increase in spite of any existing barriers.
Then, an estimated 40 percent of the people who become illegal immigrants actually enter the country legally. They get regular time-limited visas, then just overstay those visas and disappear into the community. Whether anything can be done in the context of the North American Free Trade Agreement (NAFTA) remains to be seen. President-elect Donald Trump has said that he wants to re-negotiate NAFTA. Most people focus on the commercial aspects of this, but travel to the United States could also be included in any new talks.
Much of the discourse around Donald Trump’s “build a wall” proposal centers on its impracticality. For example, the Border Patrol itself opposes much construction. Instead, it favors a huge increase in spending on a “virtual wall” (drones, sensors, and—of course—many more Border Patrol agents) that has already proved a costly failure. Opponents of immigration control and the deportation of illegal immigrants often take a similar line. How convenient.
 “Securing the border,” The Week, 16 December 2016, p. 11.
 The problem will be familiar to any home-owner who has ever tried to find a water leak.
 See: “Halloween on the Border.” https://waroftheworldblog.com/2014/08/13/halloween-on-the-border/
 The government could just slam the brakes on visas for Mexicans coming for something other than official business or demonstrable commercial reason. The State Department did this with visitors from Saudi Arabia after 9/11. Consular officers, acting on orders from Secretaries of State Colin Powell, Condoleezza Rice, Hillary Clinton, and John Kerry, have cut Saudi Arabian visitors by about 80 percent of the pre-9/11 figure.