I tried bottle rockets and the modern (weak) M80s. The geese just looked at me... "Is that all you've got?".
A couple of 12 ga shots across the pond cleared them out post-haste though. I didnt shoot at them, just near. They hardly come around much anymore, and don't stay long if they do.
Have you considered a paint gun? Stings like the begeezus but would be non-leathal unless you wanted it to be...
Jeff-