Update your server to the most recent version (the BETA version)
Make sure the people who ARE (SA) on your server are using strong passwords (and have EVERYONE change their passwords).
Lastly, you might want to look into running ts2perlmod - It has a feature to auto-kick people that get (SA) rights. You can find ts2perlmod in the Scripts forum below (or on
www.planetteamspeak.com).