_form.html.haml

/ ...
- f.inputs do
  = f.hidden_field :lock_version
  / ...

add_locking_to_foo.rb

class AddLockingToFoo < ActiveRecord::Migration
  def change
    add_column :foos, :lock_version, :integer, :default => 0, :null => false
  end
end

foos_controller.rb

class FoosController < Admin::BaseController
  inherit_resources
  include UpdateLock
end

update_lock.rb

module UpdateLock
  def update
    raise ActiveRecord::MissingAttributeError, "Lock version missing" if params[resource_instance_name][:lock_version].blank?
    super
  rescue ActiveRecord::StaleObjectError
    flash.now[:error] = t(
      'flash.actions.update.stale',
      :default => '%{resource_name} has been updated by another user.',
      :resource_name => resource.class.human_name
    )
    render :edit, :status => :conflict
  end
end