Or maybe even

```ruby

def crypt_keeper(*args)
  class_attribute :crypt_keeper_options
  class_attribute :crypt_keeper_fields
  class_attribute :crypt_keeper_encryptor

  self.crypt_keeper_options   = args.extract_options!
  self.crypt_keeper_encryptor = crypt_keeper_options.delete(:encryptor)
  self.crypt_keeper_fields    = args

  set_persistence_layer!  
  ensure_valid_encryptor!
  define_crypt_keeper_callbacks
end

def set_persistence_layer!
  include "Persistence::#{persistence.camelize}".constantize
end

def persistence
  self.crypt_keeper_options.fetch(:persistence, :active_record)
end
```