Ever heard of passwords? If people are using Jazztool, kick them out. If you are hosting an idle server, it'd better be puplic than private, sinice there is so few Jazz2player, that making those who already play joining private server would just kill jazz2.

I find this ideas about private servers to non-jdc releated events totally stupid, or just even clan server. Nobody's playing there 99% of the time, and nobody's going to enter. Even you'd have 10 clan members, it's not going to be used. TF tried, and it failed.
Another fact is that any non-jdc events should be hosted puplic because you'r not getting any people into them overwise. JDC is only possible to keep private because it is so pupulair that even people from #jj2 joins.