we could yknow
build a wall that extends down below ground
and has sensors n stuff to detect people trying to dig tunnels through
Ipquarx and Seventh already argued this off in regards to its impracticality and extreme cost, but I would also say that to build a technologically equipped and effective wall like this would be a phenomenal work of infrastructure and planning.
You're not only building a thick, deep, tall, sensor-riddled wall spanning 2/3rds the width of the continent.
You're building roads along those walls. Barracks for the men who patrol it. Settlements to house the people building it.
It would take years to build.
It would probably take longer than a term to build it. And it won't affect immigration in that time.
When the next election comes it will be a big, ugly expensive scar on the Annoying Orange governments image.
And if he loses that election, it will be stopped by the new government. And you'll have half of a useless wall, and billions of taxpayers money pissed into the wind.