Here’s my idea:
To ensure no actors and actresses are actually having sex in the sex scene, simply make sure the lenses are closely focused on the genitalia.
But, because it will be obvious then that they are not actually having sex, they should actually have sex, for the realism.
By actually having sex in the sex scene, this will ensure nobody is actually having sex in the sex scene.
q.e.d.
You know there are some scenes where the actors have admitted years later it was pretty much the real thing.
Waiting for all nudity and sex in movies to be accomplished with prosthetic props.
The violence in movies is fake, why have true nudity?