The feral cats here seem to only kill birds. If they didn't crap all over the place (scents most foul...and not welcome surprises when working a bed, or container! ), and they would only kill house sparrows and starlings, I might not be so hardened. I'll take squirrels any day. The biologist in me is fascinated by those birds and survivorship... but that same side knows they should not be here.
BTW, I pick up coffee grounds about every 3 days from a local coffee shop. I first started doing it to keep cats out of areas, but the smell wears off and they eventually return. I suspect the same will happen with squirrels but I'll keep using it as a deterrent. I already plugged every gap and hole in the fende to deter cats in back. Working so far. I still get opossums and racoons but right now they are better behaved and prefer the compost pile.