What about installing a "scarecrow," only, in this case, make it a "scaregoose." I don't know what would work. Many little aluminum foil pie plates nailed to wooden stakes and mounted variously around the pond to reflect light brightly and frighten away the geese. A fake hawk nest or eagles nest? Hawk replicas nailed in trees? Owl replicas nailed in trees? Predator look-alike decoys on the ground, coyote, bobcat? Could you install a remote activatable sound device -- an air horn or other disturbing sound -- that would shy away the geese?