What an interesting thread. I like cats but don't currently own any and have had some litter box action going on in my yard and garden. I bought some spray in the garden dept. of the hardware store that is really stinky (smells like onion and camphor, but all natural) - you just spray it around the yard perimeter and it deters the cats. It smells a little for a day or two and says you can apply it weekly but I only had to do a couple applications. Another deterent for cats is to put chicken wire under the mulch because the cats don't like the feeling of it when they scratch around to dig their hole.
I believe you were within your rights to trap the animal, but I also know from experience how unsettling it is to be at odds with a next door neighbor. Hang in there.