Have you tried the invitation feature?
It gives you the same functionality of a password protected area, only without the hassle of a password.
Just go to the settings area, and in the invitation tab, create an invite for the account you want, while keeping your account private in the original account settings (this is a different set of permissions).
The invite will be created with a 20 digit code, which only you know and you can just send it to your clients - at any time you can change the invite which will block access for the old invite link.
Let us know if you need any help setting it up.