"I used to sew my underwear up. You know the little gap at the front of your briefs? Just sew that up so nothing can pop out unexpectedly," showbizspy.com quoted the 68-year-old as saying.
The "Basic Instinct" star also said that a sex scene is all about the right preparation and rehearsal.
"Those sex scenes might look like impulse, but I wasn't some sort of rampant exhibitionist. A great sex scene is really an issue of being comfortable with the ladies in front of the camera. It's all about preparation and rehearsal. You practice, talk it through step by step," Douglas added.