AR mixin NoMethodError

I've searched on the net and found others have used mixins with AR in various ways.

I've done the following:
File: ../models/my_mod.rb
module MyMod
    def self.doit
    end
end

File: ../models/my_model.rb
class MyModel < ActiveRecord::Base
    include MyMod
    def do_this
    end
end

I believe I am using Mixins correctly, but it seems AR behaves differently.
I am getting a NoMethodError with 'method_missing' when I try to use

MyModel.doit

in a controller. What am I missing? Is this the side-effect of AR's use of
'method_missing' to generate accessors dynamically?

Thanks for any thoughts,

Long