Logic never goes very far with those consumed in the search for False Dilemmas. America can protect the borders of other countries quite effectively but somehow when it comes to protecting our own borders the task suddenly becomes "too expensive" or "impossible". It's amazing how some peoples' agenda will warp their ability to reason.
And my agenda is what, exactly?
Before you accuse others of false dilemmas, you might consider avoiding false analogies. For example: our troops overseas guard against military threats, not against Illegal Aliens. Before you consider using the DMZ of the Korean peninsula as a model, you have to acknowledge that such a barrier would necessarily have to cut across the Rocky Mountains. They would not serve as a natural barrier to Illegals, as 4Freedom had suggested. They are more passable than the mountains of Afghanistan, and we know how porous a barrier those are..
I frankly don't understand your troops fetish, and why you prefer to pursue such a bad, unviable idea, rather than getting productive measures enacted.
A re-examination of your own agendas might be in order. If you're really against rampant Illegal colonization, let's get something done, rather than bluster ineffectually about the problem.