Or shovels. 

I think we will quickly find out what we already know: Walls and fences are expensive, and by themselves do not make for great security. Smugglers are already going over, under, around, and through our existing fences. Building a longer one won't solve that. In the end, what it will really take is people. We can (and should) use physical barriers and technology (cameras, sensors, etc.), but without adequate manpower to detect and respond to intrusions, this is all for naught. No wall or motion detector is going to handcuff those who get past it. And people will get past it. Given enough time, ingenuity, resources and motivation (money), folks will figure out how.