Add this in the head tag

<!--[if lt IE 9]>
      <script src="js/html5shiv.min.js"></script>
      <script src="js/nwmatcher.js"></script>
       <script src="js/selectivizr-min.js"></script>
       <script src="js/respond.min.js"></script>
<![endif]-->

My understanding is html5shiv makes older browsers understand html5 elements like nav and section.
NWMatcher is required for Selectivzr to work (not sure about that)
Selectivizr teaches old browsers cool stuff like last-child
Respond has to be downloaded to your local folder. It allows old browsers to recognize media queries.

Put this code after the css so respond.js knows what to work with.
Sure this is over kill but if clients want cool new websites that also support old browser this is the logical way to go save your sanity.