code: function() {
          this.map.viewPortDiv.removeChild(this.zoomBox);
          this.zoomBox = null;
          this.boxOffsets = null;
          OpenLayers.Element.removeClass(
              this.map.viewPortDiv, "olDrawBox"
          );
  
      }
docs: Method: removeBox
  Remove the zoombox from the screen and nullify our reference to it.