How do you detect that monkey patching has occurred in Ruby?

How do you check that monkey patching has been done to a specific class in Ruby? If that is possible, is it also possible to get the previous implementation(s) of the attribute that's been patched?

From stackoverflow

• There are the hooks method_added and method_undefined. Garry Dolley has written an Immutable module that prevents monkey patching.

• I found this blog posting that touches on how to use method_added to track monkey patching. It's not too hard to extend it to track the methods that were patched.

  http://hedonismbot.wordpress.com/2008/11/27/monkey-business-2/:

  By using open classes, we can re-define method_added for instances of Class and do some custom stuff every time a method is defined for any class. In this example, we’re re-defining method_added so that it tracks where the method was last defined.

  #!/usr/bin/env ruby                                                                                                                                                           
  
  class Class
      @@method_history = {}
  
      def self.method_history
          return @@method_history
      end
  
     def method_added(method_name)
         puts "#{method_name} added to #{self}"
         @@method_history[self] ||= {}
         @@method_history[self][method_name] = caller
     end
  
     def method_defined_in(method_name)
         return @@method_history[self][method_name]
     end
  end