As the government shutdown continues in the absence of a compromise between the Trump administration and Congressional Democrats, the possibility President Donald Trump will declare a national emergency in order to build the border wall looms ever nearer. If indeed that is what happens, what sort of wall would President Trump prefer? And which companies would be the more likely candidates to construct it?

First some background: The U.S.-Mexican border is almost 2,000 miles long. Out of those, about 700 miles are currently fenced or barricaded to deny entry. The rest of the 1,300 miles are “safeguarded” by natural barriers, such as the Rio Grande River or mountainous terrain.

According to U.S. Customs and Border Protection, a border wall would have two main objectives: to impede and deny. “A major factor in determining where investments in impedance and denial would be most effective is referred to as ‘vanishing time,’” states the agency’s website, “which is the distance between the border and the point at which an illegal border crosser could blend into the local populace. Vanishing times are often particularly short in urban areas.”

President Trump’s statements suggest that he might favor a steel border wall in an attempt to boost the U.S. steel industry, thus hitting two birds with one stone. In a statement last week, he said, “I’ll have it done by the United States Steel Corp., by companies in our country that are now powerful, great companies again. And they’ve become powerful over the last two years because of me and because of our trade policies.”

Such a pivot toward the steel industry would be in compliance with President Trump’s team choices and foreign policy decisions. For example, the current U.S. Trade Representative is Robert Lighthizer, a lawyer and former executive in the steel industry. On the foreign policy spectrum, President Trump has imposed tariffs on steel imports in order to boost domestic production. As a result, the American steel industry has been thriving.

In a recent statement, Scott Paul, the president of the Alliance for American Manufacturing, said: “Orders are up. Shipments are up. Hiring is up. Wages are up. No matter which metric you look at, the steel industry is unquestioningly doing better than it has been for the past couple of years.”

Indeed, one of the prototypes for the border wall is made out of steel. It was shown, however, to be anything but impenetrable. Circulating pictures of the testing process reveal that the steel prototype can be sawed with household materials.

A concrete solution could be more robust in terms of penetrating, but equally passable in the absence of 24/7 monitoring. There lies the rub: no matter which company or what material is chosen for the border wall, it’s the surveillance and reconnaissance capabilities of the Border Patrol that would make it effective. Human ingenuity and desperation suggest that no wall will be impenetrable. The focus, thus, should be on what type of wall will delay more people trying to illegally enter the U.S., thereby giving the necessary time for agencies responsible for securing the border to react.