Hi, Peter-

To add to David's reply, be sure to set the objects so created and assigned to properties to .NULL. The best way, IMO, is to create a subclass of the class itself. So,

ox = Createobject( "MyCustom" )
ox.oCollection = createobject( "collection" )
...

DEFINE CLASS MyCustom AS CUSTOM
  oCollection = .NULL. 
PROCEDURE Destroy()
  THIS.oCollection = .NULL.
ENDPROC
ENDDEFINE