"Just when you thought it was safe" to do this began as ad copy for "Jaws 2"
In 1978, Scheider reprised his role as Chief Brody for Jaws 2, which featured the 
now-famous tagline: Just when you thought it was safe to go back in the water [DOC] [TLE] Amazon.com: Jaws 2 [Blu-ray]: Roy Scheider, Lorraine Gary, Murray ... [PAR] Editorial Reviews.