Some dogs dislike citrus smells, avoiding orange, grapefruit and lemon peels scattered around. Dogs also avoid chili peppers because the capsicum irritates their skin, particularly their noses. Soaking cotton balls in rubbing alcohol and leaving them in an area is also effective. Dogs dislike the smell of vinegar and ammonia, but because these substances also make effective weed killers, homeowners tend to seek out other measures to protect their lawns.
While the most effective item to keep a dog away is a fence, this is not always possible, so commercial dog repellents have different methods. Some capitalize on the natural tendencies of dogs to avoid citrus smells or chili peppers. Some use black pepper as well, which dogs also dislike. Other smell-oriented repellents target dogs that urinate or defecate in yards, masking the familiar smells that attract them to the area. Others target their sensitive hearing rather than their noses, emitting sonic and ultrasound waves that irritate them.
Dogs also avoid water sprinklers because they are frightened by the spray, noise and movement. Even if they grow used to the sight, many dogs still dislike being sprayed with water unexpectedly. Motion-activated sprinklers are particularly effective at deterring them. Dogs also dislike certain plants, such as lavender and coleus canina. Although dogs dislike garlic, the herb is also toxic to them and should not be used.