If you can and this continues to be a problem find a small office nearby. Just a single room with a door that you can lock would be enough.<p>Clarity helps a lot too, setting a simple rule that will not be broken (Monday through Friday, from 8:30 am to 17:30 pm I'm at work, and not available, sorry), goes a long way to forestalling such push-and-pull situations.<p>Being unclear can be a source of great frustration, to both parties.<p>edit: one thing you could do that might help to greasing the wheels a bit is to make sure you lunch together on workdays.