I think the numbers are a bit off, but maybe I missed something. The US-Mexican border is over 1,900 miles, closer to (or even over) 19,500 miles depending on how the fence runs. So, if you have a guard posts every 200 yards, that is around 17,000 guard posts, so 17,000 single guards per tower. If you have two guards per tower (with one in the tower, the other walking the fence, perhaps switching off every hour), you are up to 34,000 (or even 35,000) -- and that is if they work 24 hours per day and live in the tower. If you have three shift, you triple (or likely quintuple, to ensure they get days off each week as well as annual vacations). And that doesn't include the support staff needed to do administrative work, as well as hire, and train people for that guard duty. When you start adding it up, you are likely looking at around $10 billion just in personnel costs annually to man and support this fence.