I was thinking exactly the same thing. UNLESS there is at least a couple of feet of SOLID poured concrete under that expanse of 'slatted spikes', someone with a shove could burrow underneath. (And frankly as someone who lives on SAND, mother nature could undermine the 2 feet of poured concrete over a little time).
From what I heard (sorry, I can't remember specifics) they are going to go a lot further than two feet down to secure the foot of the thing. Of course, if it's slats, the border patrol is going to be watching them dig that hole with a lot of interest.