i want to remove sorting for column whose heading is Action (including with arrow images)

I am new to datatable plugin ,i am using 1.9.2,in my project one script page i had written below code for datatable this script is used along whole project ,so i can use plugin where i want

 $(document).ready(function () {     
     var oTable = $(".admintable").dataTable({ "aLengthMenu": [[5, 10, 25, 50, -1], [5, 10, 25, 50, "All"]], sPaginationType: "full_numbers",       "bDestory": true,
         "bRetrieve":true,
         "sDom": 'Zlfrtip', "oListNav": {
             sIdList: "myList",
             sWrapperClass: null
         }
     });
if (oTable.fnGetData().length <= 10) {
         $('#myList-nav').hide();
     }
});

below is html code of each page

<table id="holidaylist" class="display admintable">
                            <thead>
                                <tr>                           
                                <th>Date</th><th>Event</th>
                                   <th>Action
                                   </th>     
                                </tr></thead>
for(i=0;i<n;i++)
{
<tr><td>i</td><td>i</td><td>i</td></tr>
}</table>
 <script type="text/javascript">
 $(document).ready(function () {

            oTable = $('#holidaylist').dataTable({
"aoColumns": [ 
           null,
           null,
          { "bSortable": false }
            ]
});
});
</script>

i want sorting is disable for third row in this html page may be for different row in another page ,thats why i am writting with in page with table div Id assign data table and sorting for third column is removing ,but this code is not working anybody please help ,i am new to data table,i know this plugin is very powerful and can do anything,can any one help please......