I focus my main from my alts. I use:
/focus party1
/focus CharName (put in mains name).
That way you get a focus almost no matter what. If the main isn't on or not available, you get the person that made the party (party1). Also, that works if you change alts around, it will always give you a focus. Even if you group with other people. Things that I add, is a selective make-this-person-the-focus macro. That way you can make a person your focus easily. And all your macro don't care what people's names are.