Not suggesting this should be done, but for the sake of practical engineering argument, if a wall like this was used on the southern border, and I guess in areas where there is no hill it would have to be essentially a moat, with this theoretically save a lot of money over into nonsensically expensive concrete wall that offers a similar level of human blocking power?
https://en.wikipedia.org/wiki/Fortifications_of_the_inner_Ge...