Why would you specify the default allow rule in the ACL structure?
Suppose you want to allow anonymous access to the following actions: register, about, someotherpage
And you want to control access via ACLs to: edit, reply, profile
In the Auth component, you can set the Auth::allow property, which specifies different controller actions that you want to allow everyone (logged in and non-logged in users alike) access to. So, in your controller (can either be AppController to apply globally, or SpecificController to apply only to that controller), specify (usually in the Controller::beforeFilter() method):
$this->Auth->allow = array( 'register', 'about', 'someotherpage' );
Then Auth will only restrict access to the other pages. This should be much simpler than what you were trying to do, assuming that I read you question correctly.
HTH!