At 6'8" (203 cm) he became a leading ruckmen, but suffered three ACL knee injuries overall on both knees which limited his playing ability. The last of those injuries was sustained when his good knee buckled and twisted after running onto a small rubber circle installed in the centre of the turf ground; the circles had been installed onto grounds to assist umpires with centre bounces, but Rehn's injury, and subsequent legal action, saw the circles swiftly removed from all grounds. Rehn's injury kept him on the sidelines for most of the 1996 season after having spent much of the previous season out with the same injury. His knee injuries restricted him to just 6 games in those two seasons, three in each.