This could be done via a helper/presenter to keep the template lean.
```ruby
def google_tag_manager
  google_tag_id = Rails.application.config.google_tag_manager_id
  "<!-- Google Tag Manager -->
    <noscript><iframe src="//www.googletagmanager.com/ns.html?id=" + google_tag_id +"
    height="0" width="0" style="display:none;visibility:hidden"></iframe></noscript>
    <script>(function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':
    new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],
    j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src=
    '//www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);
    })(window,document,'script','dataLayer','" + google_tag_id + "');</script>
    <!-- End Google Tag Manager -->"
end
```