In those cases I like to structure de "derails" too. A problem with derail is when everybody is discussing subject X and it derails to "oranges" because someon

In those cases I like to structure de "derails" too. A problem with derail is when everybody is discussing subject X and it derails to "oranges" because someone just remembered to talk about it in that moment, and is afraid of not talking and forgeting it latter. If the subject is "X" and it derails to "X1", well, it would be very poor management to not this discussion arise. Participants are also responsible for keeping the subjects ordered. When preparing for a meeting (yes, everybody in the meeting should have prepared), after receiving the agenda, just see if there is some important topic that isn't covered and warn the organizer. It's very simple to update the agenda previously stating that there is one more subject. Also, it the meeting organizer doesn't already do it, remember him to leave 10 minutes at the end to "uncovered subjects", where it will be discussed briefly (and will have it's owm meeting if necessary)