Rust returned to work for Levy in 1973 as defensive coordinator for the Montreal Alouettes of the Canadian Football League. In his three seasons in Montreal, the Alouettes went to two Grey Cup finals, winning in 1974. The Patriots hired Rust as head coach in 1990, but fired him after a 1–15 season, the worst showing in team history. The New York Giants hired Rust as defensive coordinator in 1992, and he lasted one season. He spent the rest of the 1990s as a defensive assistant with the San Francisco 49ers and Atlanta Falcons.