class Model < ActiveRecord::Base
    has_many :model_options # a link table for many to many
    has_many :options,
             :through => :model_options,
             :dependent => :destroy,
             :foreign_key => 'model_id'
end

model = Model.find(id)
model.options.delete # also tried model.options.delete_all

model.options.each do |option|
   option.delete
end

class Model < ActiveRecord::Base
has_many :model_options # a link table for many to many
has_many :options,
         :through => :model_options,
         :dependent => :destroy,
         :foreign_key => 'model_id'

# Clear options records before destroy
before_destroy :clear_options

protected
  def clear_options
    options.clear
  end
end

model.options.clear