Oh dear: Rudi has thrown another wobbly. This time his tantrum is directed at a folding canvas bush chair that he is booting across the African desert. "Why can’t one goddamn bastard of a thing ever work as simply as it could?" he howls to no one in particular. The rest of us scrape stew from our bowls and watch the Southern Cross hover in the starry chaos. We have walked 125 miles across Namibia in the past ten days. We’re used to this. We make sure Rudi is nowhere near his shotgun. Someone pries open a tin of guava halves and we eat dessert.

It was meant to be a simple walk. Rudi Loutit, an African of French and Scottish parentage, worked this desert as a park ranger and wildlife researcher for three decades—a tenure that began 15 years before Namibia’s independence in 1990. Along with his late wife, Blythe, he founded Save the Rhino Trust (SRT), and their work has helped stall the black rhinoceros’s free fall toward extinction, a fate that 20 years ago seemed all but certain. Now at age 64, with the rhino population stabilizing and the Namibian government on the verge of declaring a vast chunk of habitat a permanently protected park, Rudi—a sort of Ed Abbey, Jane Goodall, and Crocodile Dundee combo—got the idea to go for a hike.

He would cross 155 miles of proposed parkland, a region known as Kunene, and survey the culmination of his life’s work, from the big-game savanna bordering Etosha National Park to the rocky badlands where the black rhino dwells, across the world’s oldest desert, the Namib, to the blinding dunes and foggy cliffs of the Skeleton Coast on the Atlantic Ocean. Even by the standards of Namibia, Africa’s second least densely populated country, this is remote territory. Kunene is bigger than Virginia but has fewer than 70,000 inhabitants. The two-week route would see no towns, paved roads, power lines, or, with the exception of a handful of huts, human-built structures. Which is the way Rudi likes it.

Like the black r...