My neighbour and I were the only non-cat owners in the street so our gardens were used as litter trays. I had a super soaker filled with a stinging nettle infuse which I used to use for fertilizer, it really stinks. The neighbours complained that there cats were coming home stinking of something they couldnt place. It wasnt really effective at keeping them away but it made me feel better. My neighbour confided in me one day that she trapped the cats sometimes and took them to the city pound as strays. If the cats were chipped it would cost the owners to get them back. We eventually bought a dog (not because of the cats) who was really territorial and once ended up in a bloodbath which wasnt what I wanted but when the owner complained I explained I wasn’t the one with a letting my dog roam the streets.