samba - Nov 2001 - setting shares

I've got a list of global shares that are up and working right now.  I 
have restricted access by using the

read list = @group_name
and
write list = @group_name

Using this, only members of the group can open the folder, and they can 
read and write to it.  However, when a user logs in that is not a member 
of the group, he can still the that the folder exists.  I don't want 
this.  How can I restrict who can actually see these resources as existing?

Thanks,
James