Hi Pat,
you can secure the conf using the numeric PIN. while adding or updating the conf you can have pin protected conf so that any one tries to join the conf, system will push them to enter the pin.
Incase you are looking for more security like no person can reach to your conf from outside via exp or only registered user can reach to this conf you can create extra search rules to allow/block the users to dial into the conf.
Thnx
Alok