A wall is only one part of a much larger set of solutions. Others include GSR, cameras, roving patrols, ground sensors, increased physical searches, etc. These are all “zone 1” type activities that occur at the boarder.
Zone 2 activities are in-country and are designed to catch illegal aliens in motion (moving to some place else in the country).
Zone 3 activities are for “resident” illegal aliens. Those that have taken up residence some where and are trying to establish a home here in the US. This can include things like requiring E-Verify be used by all employers, INS employment checks / raids, prohibiting enrollment in schools and colleges if here illegally, require the reporting of anyone sending more than $100 in overseas wire transfers, etc
“Zone 3 activities are for “resident” illegal aliens. “
These are easy to spot, they’re filing income tax forms. Seriously. My sister worked for H&R Block and had numerous illegals. (No, I don’t know about the SS numbers. But I’ll ask next time we talk.)