After you right click on your drive or folder you want to protect from other users --> select
Properties -->
Security tab... you should be able to set unique file permissions for the Restricted Access group which applies to everyone that is a member of that group ( hence the
standard user "Visitor"). If you set deny attributes
here it overrides any access you've granted earlier or from membership in any other groups (e.g. the group
users ) and the user will be denied access to the selected disk or folder.