Protecting certain model attributes from being exposed in an API

In my current project, there are business and security requirements that
prevent certain values from being exposed. I was looking for a way to
specify which attributes in a model should be protected. This is what
come up with and I would love feedback as to whether or not it’s a valid
solution and how I could improve it.

Basically, I’m following the attr_accessible style and defining an
attr_private method for setting specific attributes (or methods) as

Your thoughts are much appreciated. Thanks in advance.