The best, the most effective, and the cheapest way to solve illegals problem would be to pass a law which requires 1 year mandatory prison for each illegal employed, to the CEO of any outfit, profit or non-profit.
If such a law was passed, the wall would become unnecessary. The illegals can not dig a tunnel under the law. And those who overstay their visa (about half of the illegals) come through airports. After the employed illegals have self-deported, we can deal with the underground economy of illegals easier, because only less than 10% illegals will remain in the country.
Indeed - and no fines either, as that is just considered a cost of doing business.
Oh yeah, even if only for 30 days en toto, put 'em in with the general population - no "white collar" prisons. Let 'em get up close and personal.