In December 2007, Dunn was enlisted as defensive coordinator at New Mexico State University, serving under head coach Hal Mumme, who compiled a 7–29 record. In December 2008, Mumme was fired, and was later hired as head coach of McMurry University in Texas. Dunn joined Mumme's staff in April 2009 at the Division III school, and is currently serving as defensive coordinator.
From 2003 until 2005, he was the defensive coordinator of the Memphis Tigers football program. He transformed the Tigers defense from a unit that ranked near the bottom statistically in defense, to a top 25 defensive unit. Prior to coaching at Memphis, he was the defensive coordinator at Mississippi State from 1996 to 2002. In 1995, he served as the defensive coordinator at Arkansas.
From 1992 to 1994, he served as the defensive coordinator at Mississippi. After Billy Brewer was fired just before the 1994 season, Dunn was named head coach and led the Rebels to a 4–7 record. From 1987 to 1988, he had served as South Carolina's defensive coordinator. From 1983 to 1986, he was the head football coach at New Mexico, where he compiled a 17–30 record.