Anyone ever hear of a close hanger on the front door? Sheesh... I had a female roommate... and if she saw the close hanger, she knew to come back in a hour and vice versa.
People are going to want sex... and if they can make it happen... they WILL HAVE sex. If you don't want to hear it... then take an hour (or two in some cases) long 'break' and reflect on life or something. Sheesh... it's common courtesy... eventually it'll be your turn to send them out on 'break' too.
I really don't see what the problem is... unless they're prudes.
"The weakest soul, knowing its own weakness, and believing this truth that strength can only be developed by effort and practice, will, thus believing, at once begin to exert itself, and, adding effort to effort, patience to patience, and strength to strength, will never cease to develop, and will at last grow divinely strong."
- James Allen