what about the northern border?
What about all the boats...we could start up a ferry business...running people to the south through the gulf from the Rio Grande to the Keys.
Think about it...the closer to the Rio grande the shorter the trip...the wall would be, what...at most ten feet thick. So you toss the boat in and run about twenty feet from north of the border to the south of the border wall. You could make a bunch of trips in a day.