The Country Just Over the Fence.

A SIMPLE painted sign on a wooden board -- ''To Mexico'' -- was propped near the door in the fence, but it was the fence itself that fascinated me. Some masterpieces are unintentional, the result of a freakish accident or an explosive act of sheer weirdness, and the fence that divides Nogales, Ariz., from Nogales, Mexico, is one of them. In a lifetime of crossing borders I find this pitiless fence the oddest frontier I have ever seen -- more formal than the Berlin Wall, more brutal than the Great Wall of China, yet in its way just as much an example of the same folie de grandeur. Built just six months ago, this towering, seemingly endless row of vertical steel beams is so amazing in its conceit you either want to see more of it, or else run in the opposite direction -- just the sort of conflicting emotions many people feel when confronted with a peculiar piece of art. [ABSTRACT FROM PUBLISHER]