One summer when I was in high school, the school district decided that all the high schools in the district needed to have fences around them. They installed an ugly chain link fence around my high school. It was never completely clear to me or my classmates whether the intent of the fence was to keep us in, or keep others out. If I recall correctly, the stated purpose was to "keep drug dealers out," but they didn't seem compelled to protect junior high schools students similarly.

Whatever it's real purpose, the fence was totally ineffective in stopping students from leaving campus to eat lunch, and it didn't keep drugs out, either. I suspect the proposed wall on the US-Mexican border will be about as effective at stopping illegal immigration, or preventing terrorists from entering the US. Perhaps those proposing the wall never saw this news story about tunnels under the border. (Or this one, about a tunnel under our northern border, for that matter.)

I also can't hear about the wall without thinking of Reagan's famous "Mr. Gorbachev, tear down this wall!" line, and noting the irony of the party of Reagan now wanting to build walls, not tear them down.