Apparently it takes more than strong fences to protect nuclear power plants from terrorists -- it takes paramilitary squads with guns pointed straight at you. That's the take-home message from an advertisement which the Alexandria, Va.-based Smith & Harroff designed for the Nuclear Energy Institute. The ad, which ran in the January 26 National Journal, celebrates the "highly committed, highly trained ... expert marksmen" who stand ready to fend off any threat that might come their way. (Question: How many rifles would it take to shoot down an incoming jetliner?)