Though officially retired, Marden set sail from the Canary Islands to retrace Columbus's voyage to the New World. The Mardens concluded that Columbus made his first landfall—Columbus's "Guanahani"—at Samana Cay, not at San Salvador Island, also posited as Columbus's landfall, arguing that Columbus had landed much farther south than was initially believed. As a teenager, Marden had taught himself at least five languages as well as Egyptian hieroglyphs and later studied many others. His office is reported to have had stacks of dictionaries and grammars in different languages, including Tahitian, Fijian, Latin, Spanish, French, Italian, Danish, Arabic, Tongan, Turkish, and Maori. Marden is cited as an authority in "Webster's Third New International Dictionary" for words such as "snick," "tot," and "sevillana." Marden was an avid fly-fisherman, which led to his interest in bamboo, of which finer fly rods are made. This love led him to the bamboo groves of China's Kwangtung Province, thereby becoming, in 1974, the first "National Geographic" representative since the Communist Revolution of 1949 to return to this country. Marden observed and photographed the cultivation and processing of Tonkin bamboo in its restricted growing area in southern China. This assignment produced the article "Bamboo, The Giant Grass" (1980). "Raw material for implements of peace and war, this botanical cousin to rice, corn, and Kentucky bluegrass may be the world's most useful plant," Marden would write. Marden also recounted the under-the-table maneuverings he engaged in for entry to Maoist China. Marden made his own bamboo fishing rods. In 1997, he published his second book, "The Angler's Bamboo", which not only describes the cultivation and processing of Tonkin bamboo, but also traces the history of the split-bamboo fishing rod. Marden served as chief of the "National Geographic" foreign editorial staff, in which capacity he met and maintained friendships with King Hussein of Jordan and the King of Tonga and was knighted by the Italian government. Marden and his wife, Ethel Cox Marden, lived in "Fontinalis" (also known as Marden House), a house overlooking the Potomac built by Frank Lloyd Wright between 1952 and 1959. The spot had caught Marden's eye in 1944 when he and his wife and had been fishing for hickory shad ("Alosa mediocris") along the Potomac, near Chain Bridge.