I mean "the wall" as an immigration enforcement mechanicsm. A fence in the middle of the desert does nothing. People have tried to sit down and sketch out what would be needed to actually catch immigrants everywhere, and the law enforcement costs are ridiculous (and in pursuit of an action which would objectively hurt the economy, no less).

Here's a start https://fieldofvision.org/best-of-luck-with-the-wall

> A voyage across the US-Mexico border, stitched together from 200,000 satellite images.