>> see to it that almost all of southern border has such a wall...
Last time I checked, Mexican immigration is reversed - iow more Mexicans leaving the US than entering. I think a lot of illegal immigration is from further South now. So if a wall is needed, probably it should be on Mexico's other borders rather than the US-Mexican border.
"... They ne'er cared for us
yet: suffer us to famish, and their store-houses
crammed with grain; make edicts for usury, to
support usurers; repeal daily any wholesome act
established against the rich, and provide more
piercing statutes daily, to chain up and restrain
the poor. If the wars eat us not up, they will; and
there's all the love they bear us."
-- Shakespeare: Coriolanus, Act 1, scene 1
