How to avoid inserting date which not present in Month Feb Like 2013/02/29

protected bool CheckDate(String date)
       {
           try
           {
               DateTime dt = DateTime.Parse(date);
               return true;
           }
           catch
           {
               return false;
           }
       }

<script type="text/javascript">
function checkdate()
{
   var validformat=/^\d{2}\/\d{2}\/\d{4}$/; //Basic check for format validity
   var returnval=false;
   var inputvalue=document.getElementById("txtdate").value;
   if (!validformat.test(inputvalue))
   {
      alert("Invalid Date Format. Please correct and submit again.")
   }
   else
   { 
      //Detailed check for valid date ranges
      var monthfield=inputvalue.split("/")[1]
      var dayfield=inputvalue.split("/")[0]
      var yearfield=inputvalue.split("/")[2]
      var dayobj = new Date(yearfield, monthfield-1, dayfield)

      if ((dayobj.getMonth()+1!=monthfield)||(dayobj.getDate()!=dayfield)||(dayobj.getFullYear()!=yearfield))
      {
         alert("Invalid Day, Month, or Year range detected. Please correct and submit again.");
      }
      else
      {
         returnval=true;
      }
   }
   if (returnval==false) 
   {
      input.select();
      return returnval;
   }
</script>

<asp:TextBox ID="txtdate" runat="server" Width="200px"></asp:TextBox>
<asp:Button ID="btnSave" runat="server" OnClientClick="return checkdate(this.txtdate)"  onclick="BtnSave_Click"
                                    Text="Save"   />