This plugin allows you to quickly kick all players, that are not in your clan and set a password on the server, to hold a practice. When used, all players will get a warning, telling them they will be kicked in 15 seconds if they are not in your clan, and so will they be :)
Be carefull to spell your tag right, or all your members will be kicked too! Note that anyone wearing your tag wont be kicked, even if they are not in your clan!. Also note, that immune admins wont be kicked neither.