The solution to preventing cats turding on your lawn is not to poison or maim them - these are beloved pets of families who probably have a litter box indoors sitting unused because the cat makes its own decisions. The best option is just to discourage them from using the area. Citronella oil is one option although anything that the cat may potentially lick off their fur during grooming should be considered a no-no. Water is a good deterrent and is friendly to your garden and other wildlife. Half the time the problem is scent - particularly with dogs (Foxes are a breed of dog for example) as they will follow scent clues and repeatedly use an area as their toilet based on the scents - the only way to stop this is to remove the scent. This is easily done on paved areas, not so much on lawns. The most appropriate and least cruel options are to purchase something specific from a garden centre - Lion dung, cat repellent, Movement sensors whatever. There are no short cuts. Please stop posting advice related to poisoning cats - if my own beloved cat was poisoned it would break my heart. I'd love to neg rep anyone posting about cat poisons because you are essentially facilitating cruelty - I didn't know Starfish poisoned cats, and if I were a nasty individual I could now use this information to do harm. It would be far better if you kept information like that to yourselves.
Where foxes are concerned, you might like to try planting Rosemary - apparently dogs don't like the scent. Doesn't work for cats though - my cat is fine with our rosemary plants.
I wouldn't dream of poisoning cats. No fun in that, much better to watch my dogs chase them. :rolleyes: