We have had 7,458 miles of unguarded, unfenced border with our neighbors for the last 235 years we've been in existence. Guarding it, fencing it would not only be expensive, it would be stupidly expensive and totally ineffective. Have any of you watched someone who is in the habit of jumping tall chain link fences go over one? It's worse than watching a car thief start a car faster than you can get out your keys. Plus it's even easier to cut it, or bend it or prop it... How effective was the "Great Wall of China"?