Ben, the marker, once dropped on the map follows it along like a puppy follows its owner.
The puppy has knowledge of its owner, and the marker also knows it's owner. To delete a marker from a map, you tell the marker ( not the map) to delete it's knowledge of its owner ... The map.
Learn more here:
https://developers.google.com/maps/do...
Also.. The syntax is
omarker:setmap( null ) ;
Where 'omarker' is the name of your marker. If you are not already doing so, if you create multiple markers ... You need to store them in a persistent array ( not local to your UI or method ) ... And then when you refresh your map, spin through the array ... Remove the map from the marker using the syntax above, kill the aray, and then Rebuild a new array with the new markers.
Example code on the Google website ...( see link above )
Best
Bruce