The slingshot is a great idea. I have gravel pathways, so an infinite supply of different sizes of rocks, too! I definitely want the one with the laser sight.
My son got me a great pellet gun. It's spring loaded so pretty quiet, and shoots 6mm biodegradeable (not really) pellets. It fires fast and accurately enough to hit something 40ft away, and get their attention, but does not hurt the squirrels which I have hit from only 10ft away. They sure do jump, though! My proudest shot was the red-tail hawk that sits on top of the power pole and hunts my songbirds. Hit him right in the belly, he flinched, fluffed up and flew off. The desired result.
As far as noise makers, I'm finding the raccoons are pretty scared by my banging on an empty watering can. I have two big plastic ones, and last night I banged them together, which made a great sort of 'native' noise, I thought . . . music to scare critters by??
Btw, in auld English (Or was it Celtic?) I think any mountain can be called an "alp", hence the word "alpine" to describe high places.