Despite a successful practice, by 1983 he was in financial difficulties from bad real estate investments and gambling debts. Becoming involved in a counterfeiting scheme, he printed $6 million in U.S. 100-dollar bills, some of which he stored in ice chests buried in the back yard of a house he owned and rented out. Charged along with five others, he served two-and-a-half years of a five-year sentence at the Federal Correctional Institution, Texarkana. Upon his release in 1986, he regained his dentistry license but struggled to rebuild his practice. In 1995, he was hired as a dentist at the Louisiana State Penitentiary, initially as a contractor. At the time, the dental clinic in the prison was in chaos; many dentists refused to work there and inmates were often unable to make appointments. Cannon reorganized the dental program with great success and was soon hired as a full-time employee. Warden Burl Cain, impressed with Cannon's work with the dental program, put him in charge of the prison's entire medical system. Cannon remained the resident dentist at the penitentiary, where inmates typically call him "Legend".