undef_method metaprogramming confusion

gistfile1.rb

class Foo
  def foo
    puts "foo"
  end
end

class Bar < Foo
  undef_method :foo
end

Foo.new.foo    #=> prints "foo"
Bar.new.foo    #=> raises NoMethodError


class Baz
  def self.baz
    puts "baz"
  end
end

class Quux < Baz
  # ...???  how do I undefine self.baz?
end

Baz.baz       #=> prints "baz"
Quux.baz      #=> I would like this to raise a NoMethodError