> I'm looking for a way to prevent the redefinition of a method. I'm able
> to check when a method is defined (redefining Module#method_added) but
> I'm unable to halt the new definition. I'm also unable to know if the
> method is already defined or not.
You can freeze the class to avoid having any redefinition on it:
	MyClass.freeze

This is not valid at method-level though
-- 
Sylvain Joyeux