The 1.5-mile strip of triple fencing that cuts through suburban San Luis is the most impenetrable, says Bernacke.
That's because the three walls are separated here by a 75-yard "no man's land" – a flat, sandy corridor punctuated by pole-topped lighting, cameras, radio systems, and radar units, where unauthorized migrants can be chased down by border agents.
The triple-layer fencing begins at the San Luis port of entry, one of a handful of formal checkpoints where cars and trucks from Mexico line up, waiting for the US border patrol to inspect them for illegal contraband or migrants before they cross over. One-and-a-half miles east of San Luis, the triple fencing gives way to double fencing for about five miles, after which come another 39 miles of so-called "primary fencing" – a combination of steel mesh and steel panels fitted over bollards, or small metal and cement pillars, that stick up from the ground.
"Back in 2005 when President Bush came here, newspapers were writing that Yuma was the most dangerous place to live – and he came in and said, 'I am going to fix this' and he did," says Yuma Mayor Larry Nelson.
Conversations with residents and business owners in this town suggest the fence is not such a hot-button issue. But, violent drug smugglers aside, neither has the flow of illegal immigrants been a big issue, observers say.