If you have a cat or cats, you likely have experienced cats choosing inappropriate locations for urination. Although un-neutered male cats may simply be marking territory, both neutered and un-neutered males and some female cats may simply choose a place to urinate outside of the litter box. In some cases, some citrus sprays can deter cat urination.
Cats tend to dislike the smell of citrus. A number of commercial cat training sprays contain citrus. However, a commercial citrus cleaner or a commercial citronella spray may have the same deterrent effect. If your cat is urinating in a potted plant, consider placing citrus peel in the plant as a deterrent. In some cases, simply rubbing an area with orange peel, ensuring you break the surface of the skin to facilitate citrus oil transfer, can work.
If your cat is urinating against a wall and is male, he is likely marking his territory. Scrubbing the area with citrus cleaner and placing some oranges nearby may work as a deterrent. However, un-neutered male cats have a stronger instinct to mark territory than other cats. Citrus may either not be a strong deterrent or may simply trigger a move to a different location for marking.
The solution that will work best will depend on the location and the cat. In most cases, a commercial citrus deterrent will work well and won't be objectionable to people. Some citrus cleaners may have too strong of an odor to be usable on something like a bed. In some cases, citrus peels or home made sprays may be mild enough not to disturb people, but strong enough to be objectionable to the cat.
If the location isn't one where you will be sitting or sleeping, like a bed or chair, citronella spray works very well to deter cat urination. Citronella spray or oil may be too strong a scent for use on a bed, If the cat is urinating in a pot, citronella spray or a homemade spray using citrus peels and cayenne pepper can also be effective. This can also work for cats urinating in outdoor gardens. Many commercially produced cat deterrents, especially natural and organic deterrents, contain citrus and may work well for deterring cat urination.