Whether the cats coming onto your property are one of the tens of millions of feral cats estimated to be roaming the U.S., or a couple of the neighbor's wayward out-of-doors tabbies, cats that stray into your yard and root up your garden or dig through your trash are not necessarily welcome. There are ways to discourage felines from intruding on your property that do not involve traps or costly electronic deterrents.
If it is easy for a cat to get into your yard and your yard is small, consider constructing a simple fence made from chicken wire. To keep cats from climbing over it, lean the fence outward. If you already have a wire fence surrounding your yard, stretch a taut string or length of wire just above the top of the fence. This will deter cats from trying to walk along or crawl over the fence.
Consider purchasing the garden plant Coleus Canina, sometimes referred to as "Scaredy Cat" or "Scardy Plant." Cats will avoid this plant. It is an attractive plant with appealing foliage and blue spiky flowers, but it releases an odor that deters cats. Humans can only smell the plant when it is touched. The plant is an annual, so this may be a good solution for the warmer months.
For the least expensive solution, try a few natural scent repellents. Cats do not like the smell of citrus, so orange, lemon or grapefruit peels scattered around your house may deter them. Coffee grounds, too, give off an odor cats find unpleasant. These can be sprinkled in areas where you don't want cats to go, such as gardens or flowerbeds. Lavender oil, citronella oil, and peppermint oil are also scents cats find disagreeable.