Had a mate that set up "party poppers" on tripwires for the neighbours dog.
Only like $2 for 24 of them in the supermarket here(and I reckon it would only have to get each cat once), but I'm not sure if the cats would push hard enough to pull the trigger. If not, you might have to set up tripwires with drop weights that do the actual firing.
A coke bottle of water balanced on a stake, trip wires connected to the bottlecap, and then connected to the party popper strings. Only takes a tiny brush to unbalance the bottle, and the heavy bottle falling off pulls the strings on the party poppers, spraying confetti at the cat and making a loud bang.
$3 to set up.
Snare is still cheaper and a guaranteed fix though, and if the cats and wandering round crapping everywhere, then they are definitely wandering around killing shit, as is their instinct, no matter how well fed.
No dramas with an inside cat, or in an enclosure, but semi-feral is irresponsible IMO.
Think Mogwai.
One of the best natural cat deterrents is educating the owner of the offending cat.
Exactly!