People have been using the dog's strong sense of smell for centuries for searching and hunting. This super sense can be used another way too -- to get Fido to stay out of the garden and off of furniture.
Nearly all dogs dislike the smell of citrus, whether it's oranges, lemons, limes or grapefruit. Fortunately, most people enjoy the fresh smell of citrus and it's not dangerous or harmful, making it handy for use around the house and yard. Fresh citrus peels make a great temporary repellant. Mix concentrated lemon juice with water for a repellent spray that is safe to use almost anywhere. Test the citrus spray first on sensitive plants and fabrics that could be discolored.
Capsaicin, the chemical that puts the spice in chili peppers, is irritating to a dog's sensitive nose. Because of this, most dogs will avoid anything that smells like a chili pepper. You can rub or sprinkle cayenne powder and dried chili powder directly on objects and areas where dogs are unwanted. You can also mix it with water for a spray solution that will repel dogs. Although chili pepper repellent is not toxic, it can irritate the eyes, nose and throat. Touching it with your hands and then accidentally touching your eyes can cause a burning sensation. Take caution to use chili pepper deterrent where children will not come in contact with it, or it won't be breathed in by humans, especially anyone with breathing problems.
Dogs have incredibly sensitive noses, and seem to turn up their nose at the smell of vinegar even more than some humans. Place vinegar in small open containers, soak it into a rag or spray it around areas where dogs are not wanted. Although it is safe to use around the house to keep dogs away from furniture and other objects, most people do not want their home to smell like vinegar, so it is more suited to outdoor use. Test it first on sensitive or delicate plants, but generally it is safe to spray a vinegar-water mixture anyplace in the yard or garden.
Mothballs don't really smell good to anyone, but dogs especially hate the scent. They are good for repelling dogs from an entire area, but use them with caution. Mothballs are poisonous to most animals and to humans. Place them out of reach of pets and children.
Like chili powder, the smell of ammonia is irritating to a dog's sensitive nose. Spray ammonia on objects or soak it into rags or cotton balls. Only use it in well-ventilated areas, since the strong fumes can also be irritating to humans.
People seem to either love or hate the smell of rubbing alcohol. Dogs aren't so divided on the issue and don't like the strong scent. To make the scent last a little longer, don't spray rubbing alcohol, but soak cotton balls in it and place them in areas you want dogs to avoid. Make sure the cotton balls stay out of the reach of children.