Building such a wall as this, has another advantage I've not seen mentioned here.
Iron poles can be made at least 50' maybe 100'+.
So how far under ground would the poles go?How far under ground can the cartels dig tunnels?
It seems to me that it would cost less to drill a hole very very deep and insert a pole 50' under ground-30' above ground. than to dig a 50' trench to fill with rebar and concrete.
We can insert these iron poles deep enough to block all of the tunnel digging at the same time.
Winning!