Fencing Off Kakadu

Adam Bowman's "whole life and love," he says, is Kakadu. For 12 years he's been taking tourists into the Northern Territory's world-famous national park, aiming to teach his mainly European clients to love the wild land as he does. A favorite spot on his three-day safaris has long been Twin Falls, where a sandy beach borders a deep plunge pool. After swimming about 250 m up a winding gorge to the pool, eating lunch while afloat on air mattresses was a big hit with travelers, says Bowman: "Most said it was the prettiest waterfall they'd ever seen."

He won't need...