One way to keep dogs or cats away is to use scent as a repellent. Dogs and cats have sensitive noses, and certain smells may irritate them and keep them from coming near the treated area. However, you should test these treatments with your pet before use, because some animals react to scent in different ways.
One way to keep both dogs and cats out of an area is with citrus. Most dogs and cats abhor the smell of lemons, limes and oranges, and they will avoid treated areas. You can use citrus peels outside in the garden to prevent digging, and you can spray interior areas with diluted lemon juice to keep your pets away from delicate furniture. Test your repellent spray on an inconspicuous area first, however, as the acid in the juice may damage or discolor fabrics.
Vinegar is another powerful repellent for both cats and dogs. The pungent liquid is too strong for their sensitive olfactory systems, and even after it dries, it can serve to ward away animals. Unfortunately, most humans dislike the smell of vinegar as well, making it more suitable for outdoor use than indoor applications.
Cayenne pepper and other substances that contain capsaicin make good animal repellents. Capsaicin causes a burning sensation when it touches taste buds or mucous membranes, ensuring that dogs and cats will keep clear of any treated area. Capsaicin also can be an irritant for humans, so never use it around people who have respiratory illnesses or in areas where children may encounter the substance.
The camphor in mothballs produces a strong odor that few animals find pleasant, making them a good deterrent for dogs and cats. Unfortunately, mothballs are poisonous if ingested, so you should never use them in areas where pets or children may have access to them. Placing them out of reach or in secured and ventilated containers can allow their pungency to work while preventing accidents.
Ammonia is another repellent that can work for both cats and dogs. Ammonia is one of the components of urine, and the powerful smell may trick your pet into believing an unfamiliar animal has marked this area as his territory. Ammonia can cause eye and nose irritation in high concentrations, so you should only use it as a deterrent outside and in small quantities.
Many strong-smelling plants are toxic to animals, causing dogs and cats to avoid areas that bear those distinctive smells. Eucalyptus oil is one smell most pets will shy away from, and a few drops of the concentrated liquid can serve as a long-lasting repellent.