lol - an excellent, rational and unexpected reply
As a damaging, invasive species I'm all for controlling them, but am mindful of how I convey this opinion as most urban-dwellers seem to deny any issues and cry barbarism just because they're furry. I'm sure they're less cute when they're casually chewing the face off a fledgeling blue tit..
I think anything to be done to prevent feeding them is a good thing; as you're only bolstering their numbers and as I'm sure you're well aware they can be very damaging to other flora and fauna.. not to mention the associated cost in bird food and knackered feeders. I think the only thing you can do to keep them out of the garden is remove access to all food sources..
Yes; while a generation or two ago those in rural communities wouldn't have batted an eyelid at youths off down the fields with an airgun / shotgun slung over their shoulders to get something for dinner, times have definitely changed. I agree that a catapult / slingshot is less politically-charged; but also a hell of a lot harder to hit stuff with and of course nothing deserves to suffer.
I think many would be shocked by the number of squirrels about - you might only see one or two in the garden at any one time, but chances are there are a lot more. A guy I used to know a couple of villages across started shooting those in his garden and I think he managed about 60-odd in a year.. that was in a relatively built-up location too - not out in the sticks.
Sounds like you have the privilege of a lot of nature on your doorstep - not much in the way of water around here but I occasionally find amenible toads in the garden, while we get regular woodpeckers, nuthatches and other interesting birds. I occasionally see foxes and deer on the land adjacent to the house and when I'm out for a walk. I actually saw a live hedgehog a while ago too; which I think was a first!
The "squirrel proof" feeders will spill their guts if knocked off; which of course is another concern. We had one that wasn't hung far enough away from the wall and they eventually chewed around the ports and knackered it. Your idea of the baffled line sounds like a grand idea if you have the space - unfortunately our garden is too small to really position anything outside of jumping range...