It is so wonderful that you are making sure no more feral cats come along. Outside cats are such a danger, they spread disease and are major predators of songbirds. All the cats I've owned were adopted strays, although they were kept indoors at all times after adoption. We also have neighbors who claim that a cat is their pet, but never allow it indoors or pay it any attention. They simply leave food and water on the porch. In the summer the cat comes over and sprays our front door, apparently thinks our cat is competition. Year round it uses our backyard as a litter box.