Bonnie, I have large oak trees all around my house, and finally resorted to using bridal veil netting to keep the leaves and then the flowers out of my pond. It's cheap, and comes in fairly wide widths at the fabric store. You might even get lucky and find a bridal veil for next to nothing at a thrift store. Other netting just wasn't fine enough to keep those tiny dried up flowers out of the water but the veil netting works great. If too much stuff collects on it, I can blow it off with the leaf blower and still the tiny flowers don't get through the net.
I put it over the pond as soon as the trees start dropping leaves and take it off once all the flowers are down. I figure why have a pond if you have to keep netting over it all the time??
As for shooting things, I have a spring loaded pellet gun that I 'discourage' critters with. It gets their attention, but won't kill them, and doesn't attract any attention from neighbors. If you go that route, get one with a high muzzle velocity, because the cheap ones don't even phase a squirrel - they get hit in the butt and turn around like "is that all you got??".
The one I have shoots straight for at least 50ft. and I've hit a hawk on top of a power pole with it before. He ruffed his feathers and flew away, just what I was hoping for since he was 'hunting' around my bird feeder.
