To stop a cat from pooping in your garden, sprinkle cayenne pepper in it – all over the exposed dirt. You will have to repeat this every time it rains. But, it is a heck of alot cheaper then the chemicals they have out there to do the same thing. They (the expensive chemicals) also need to be repeated when it rains. You can get the XL container (~ quart sized) at the grocery store for $5 or less.