If they can’t get a wall up, how about a thousand miles of Concertina and razor wire! Not just ole roll but maybe a dozen or so.
It may slow then down a little.
Or they can get a green card and make it legal.
Mine fields along the border would work rather well I would think. Might keep a few other groups out as well.
Strange why these people all go “north” when there is a South America too? (sarc)