I’l run my military potrol lines as far on the edge of those towns northern borders, but still within Mexico. Those towns themselves will make “keeping the illegals to Mexico” easier - sentry points just direct folks back into town.
In San Diego, Tijuana (that's the one on the right) buts up along the border fence for 15 miles. That's how it is typically, one big urban area with a fence down the middle (in Texas, its a shallow river).
