In 2006, Rehn joined the Brisbane Lions as ruck coach where he helped develop Brisbane's young ruck division including Jamie Charman, Cameron Wood and Matthew Leuenberger. In 2011 Rehn coached South Australia in the 2011 State of Origin Slowdown to a 17.10 (112) to 17.9 (111) victory over Victoria in a charity match at the Adelaide Oval for the Little Heroes Foundation and the Reach Foundation youth charities started by former Melbourne ruckman and 1991 Brownlow Meadallist Jim Stynes. On 19 October 2011, Port Adelaide announced that Rehn would be an assistant coach at the club.