navigator.geolocation.watchPosition properly

I am getting problem in user location fesching

Problem is that when I move device with current location the older one marker is not remove, insted it creates new marker every time, I ha ve user clearwatch () but its stop displying map also 

Here is my code snap

        body { height: 100%; margin: 0; padding: 0 }

    #map_canvas { height: 100% }

    </style>

    <script type=“text/javascript”

    src="[http://maps.googleapis.com/maps/api/js?key=]]…APIkey…[&sensor=true">

    </script>

    <script type=“text/javascript”>

    var accuracy;

    var watchID;

var geoLoc;

    function initialize()

        {

            var locationMarker = null;

            var myOptions = {

                center: new google.maps.LatLng(]]…USER_LOCATION.LATITUDE…’, '…USER_LOCATION.LONGITUDE…[[),

                zoom: 1,

                mapTypeId: google.maps.MapTypeId.ROADMAP

            };

            var map = new google.maps.Map(document.getElementById(“map_canvas”),

                                          myOptions);

                             watchID= navigator.geolocation.watchPosition(getLocation,unknownLocation,myOptions);

                                     

                                           

                                             function getLocation (pos) 

                                                {

                                                      var im = ‘http://www.robotwoods.com/dev/misc/bluecircle.png

                                                       var latitde = pos.coords.latitude;

                                                    var longitude = pos.coords.longitude;

                                                    var myLatLng = new google.maps.LatLng(pos.coords.latitude, pos.coords.longitude);

                                                    

                                                    var userMarker = new google.maps.Marker({

                                                            position: myLatLng,

                                                            map: map,

                                                            icon: im

                                                        });

                                           alert('Your current coordinates (myLatLng) are : ’ + latitde + ', ’ + longitude);

                                                };

                                                window.setInterval( function () {

                                                getLocation();

                                    }, 

                                5000 

                                navigator.geolocation.clearWatch(watchID);  

                            );    

                                       

             function unknownLocation()

                  {      

                    alert(‘Could not find location’);

                  }

                

          var image = new google.maps.MarkerImage(‘localhost/streetculture/images/1/img1.png’,

                                                    new google.maps.Size(25, 28),

                                                    new google.maps.Point(0,0),

                                                    new google.maps.Point(12, 28)

                                                    );

            

            ]]…markerString…[[

         }

        </script>

        </head>

        <body onload=“initialize()”>

Please guide me