How do I prevent placemark(with same lat & long) duplication?

[Jung Soh]

well, I can already create placemarks on click! what I want is to
prevent the user from creating another placemark with the same lat and
long values. Here is my initial code based on google earth apis.
Somehow it doesn't seem to work.. How do I make sure that the user
wont create a new placemark on the same lat long? I thought if
(event.getTarget().getType() != 'KmlPlacemark' &&
event.getTarget().getGeometry().getType() != 'KmlPoint' should do the
trick.. Any idea? T_T

google.earth.addEventListener(ge.getGlobe(), 'click', function(event)
{
if (event.getTarget().getType() != 'KmlPlacemark' &&
event.getTarget().getGeometry().getType() != 'KmlPoint') {
event.preventDefault();
//create a place marker for the pole
var poleMarker = ge.createPlacemark('');
var point = ge.createPoint('');
point.setLatitude(event.getLatitude());
point.setLongitude(event.getLongitude());
poleMarker.setGeometry(point);

ge.getFeatures().appendChild(poleMarker);

}
});