Condom analogies.

Along the lines of (paraphrased):

"Saying that condoms in schools promote sex is like saying that umbrellas promote rain."

- Nicholas D. Kristof, New York Times, 11/26/03

A reader of National Journals' Hotline (subscription only) asks:

"Isn't a 700-mile fence on a 2,000-mile border a little like only wearing the bottom half of a condom?"