In 1933 Cairns joined the Police Force in order to have more time for athletics. He soon became a detective and gained notoriety working in a special surveillance team known as "the dogs" shadowing squad, where he was involved in a number of dramatic arrests. While working, he studied at night and completed an economics degree at the University of Melbourne. He was the first Victorian policeman to hold a tertiary degree. In 1939 he married Gwen Robb (died 2000), whose two sons he adopted.