Shannon achieved a record of 192-34 in 20 seasons at East St. Louis. In 1985 he was selected as the USA Today High School Football Coach of the Year along with taking the High School Football National Championship. Shannon accused the school district of condoning corruption. He claimed the athletic director stole from the district. He left in 1995 after the school board backed the athletic director, who later pleaded guilty to stealing $90,000 from athletic accounts. Janet Reno awarded Shannon the United States Attorney General Award, an award rarely given outside of law enforcement, for his efforts to fight corruption. He coached Alton and Christian Brothers College High School before retiring from coaching in 2007 at the age of 63.
