Served as head coach of the Denver Broncos from 1993 to 1994, the Buffalo Bills from 1998 to 2000 and the Dallas Cowboys from 2007 to 2010. He then went on to work as defensive coordinator of the Houston Texans from 2011 to 2013, finishing the 2013 season as the team's interim head coach.
He held a record for career assisted tackles at the University of Houston, where he played as a linebacker.
He coached the 2007 Cowboys team, which went 13-3, but lost to the Giants in the divisional round of the playoffs.
He helped develop Cowboys quarterback, Tony Romo but they could never break through and win a big playoff game together.