Most active in the 1960s and 70s, Sondern supplied cartoons for A New Answer Book (1977) and illustrated Three-Horn the Dinosaur, an adaptation of Pinocchio, Colorforms ABCs, and Finnerty Flynn and the Singing City by Clark Gesner. Sondern also illustrated greeting cards and, in adult fiction, a novelization of Rod Serling's Requiem for a Heavyweight. He still contributed to art shows in Pennsylvania as late as 2008.