Rails extension to add Permalink functionality to any model. To use, place in /app/models/extensions/permalink.rb

example_model.rb

class ExampleModel < ActiveRecord::Base
  # include the module
  include Extensions::Permalink

  # make sure there's a method named "unicode" that
  # returns the string you'd like to sluggify
  def unicode
    self.name
  end

end

permalink.rb

module Extensions
  module Permalink
    extend ActiveSupport::Concern

    included do
      before_validation :generate_permalink

      validates :permalink, :uniqueness => true

      def to_param
        self.permalink
      end

      def generate_permalink
        if self.new_record? || self.permalink_changed?
          orig_p = self.permalink || self.unicode.parameterize
          p = orig_p
          i = 0
          while self.class.find_by_permalink(p)
            p = "#{orig_p}-#{i}"
            i += 1
          end
          self.permalink = p
        end
        true
      end
    end
  end
end

The model must have a 'unicode' method, which returns the field to be used as the permalink.