To get around a wall, you tunnel, and line the tunnel with rubber – so it does not show up under ground radar – a stealth tunnel. The Roman's use their walls for tax collection – not to keep people out.
The border between the US and Mexico is already as porous as Swiss cheese – with all the deep basements linking the two counrties. Or you fly across in a microlight – you ship back to Mexico. A nice little business – crossing the Trump Folly.
And you have to station gunmen every 50 metres along the Wall. So you have the situation where the land of the free fires, to keep people out.
And you have to secure your sea borders, along a 2069 miles line. To keep out ships from YOUR bankers. China owns 60% of the US. You are really going to set off a tariff war – with the people who own you?
You are far better off, using steam plasma tubes to do Molecular Nuclear Fusion, and generate free power. https://plus.google.com/116729936523681207525/posts/UWdfqZBdN8z