Or may be just have a div appear after 10 minutes of constant activity which says "OK, now enough is enough. Get back to work. (Signed PG)" Signed PG is an ext

Or may be just have a div appear after 10 minutes of constant activity which says "OK, now enough is enough. Get back to work. (Signed PG)" Signed PG is an extra effect: Many take your words religiously :)