Cahill spent two seasons at the Collingwood Football Club in the VFL (1983–84) where he led them to 6th in 1983 and 3rd in 1984. He then returned to Adelaide where he coached West Adelaide in the SANFL (1985–87), taking the club to 3rd in his first season and the league Night Premierships in 1985 and 1987. But it was Port Adelaide where his heart lay and he returned to Alberton in 1988 and led the club to six more premierships before ending his SANFL coaching after 14 rounds of the 1996 season to move on to coach Port in 1997 and 1998 when they were admitted into the AFL.