In order to stop players from joining, as stated you'll need to set the join power on the channel higher than the user's join power. However, on our TeamSpeak you're unable to modify any channel's join power or create your own channel because our network is open for everyone.
Moderators can create their own temporary custom channels, so you may considering asking a Moderator to supervise you if you need your own private channel to do a recording or play with friends without being disturbed.
In all cases, if you find that someone's purposely trying to disrupt your channels, don't hesitate to poke a Staff member and we'll come resolve the issue.
Since I feel the question has been answered sufficiently I'll be locking the thread. If you have any further comments, questions or concerns please don't hesitate to personal message myself or another staff member. Enjoy your time on the MCGamer network and thanks for making use of our TeamSpeak. :]