I have no moral or philosophical objections to a wall, but as Mr Ellison's post points out, it's not really clear how effective it's going to be. And your projected cost ($4G?) is staggering. I've driven I-10 from California to Florida and that border country is a vast, barren area. The environmental costs of such a project would be unacceptable (not so much the finished wall itself, but the construction effort required to erect it) and the potential for pork barrel and boondoggle is colossal. And who's going to build it? The construction industry is more and more dominated by immigrant labor! And here in Florida, we have a huge immigration problem too, they're coming in by jet, not across a border. I think this is one problem not amenable to a technological solution.

There's a lot of construction in Florida, always has been, (we have no natural resources except real estate), and it has always been a major industry. When I was a student, construction work is how we earned money between terms, there was always a job open pouring concrete or tying steel (I was a form carpenter's helper and a golf course construction worker on summer breaks), and the work crews were about 80% hippies, about half of them college kids. Florida is a right-to-work state.

Today, we are told "Americans won't do that kind of work" so the crews are South American illegals and the skilled trades are often Euro green-card holders. Rubbish, these people will just work for less and they are a more docile work force, too scared to "cause trouble" and not in any position to run off after a better offer. The "labor contractors", middlemen between the construction outfits and the labor force, keep things running smoothly. It's not a pretty system.

I may be wrong, I'm certainly not an expert in this field, but I think the key to this problem is to cut off the demand, not the supply.