Admittedly, I have been confused by the concept of a border fence from the beginning, but this didn't really clear things up. Evidently Tom Tancredo (R - Crazytown) wants to build the fence somewhere other than the border (h/t TPM).
During the hearing, he told the Brownsville landowners, "I suggest that you build this fence around the northern part of your city..." implying that all of Brownsville should be on the Mexican side of the wall.After extensive research I was able to verify that Brownsville is in fact located within the borders of the United States.
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See it there, in the bottom left, Mexico on one side of the line, United States on the other (and Brownsville) side.
Assuming we follow Tancredo's advice, we either have to cut off a city from the rest of the country, or build a fence with a few road sized holes in it (try keeping a dog in your yard with one of those, you'll see it's not really that much of a barrier).