Upon graduation from South Dakota State University in 1956, Roger taught PE and started the second wrestling program in South Dakota at Spearfish High School. In 1961, Denker moved to Casper, Wyoming, to teach history, and continued his coaching career.

In 1963, he made the move to Warrensburg, Missouri, to be the head wrestling coach (1963-1981) and assistant football coach (1963-1972) at the University of Central Missouri.

Denker guided the Mules' wrestling program to national prominence during his 17-year tenure as head coach. Highly respected as a coach, educator and administrator, Denker coached the Mules to seven Mid-America Intercollegiate Athletics Association championships and six Top 20 finishes at the NCAA Division II Championships. Three times he was voted MIAA coach of the year. The Mules had 10 All-Americans and 63 national qualifiers under Denker. His 143 dual match wins are the most in Mules' wrestling history.

He also taught in the physical education department and served as acting athletic director for the 1980-81 school year.

Denker retired from coaching after the 1980-81 season and retired from teaching with the rank of professor emeritus in 1993.

The Mules have one of their open tournaments each season named in his honor.