To make a homemade dog repellent, HowStuffWorks recommends using either citrus, vinegar, cayenne pepper or ammonia to keep dogs out of the garden. Although the citrus and pepper are safe for use in the garden, gardeners must take special precautions when using vinegar and ammonia in flowerbeds.
To keep a dog out of the garden, HowStuffWorks recommends putting orange or lemon slices throughout the garden. It also suggests making a mixture of these citrus fruits and water and spraying them on the furniture to ward off dogs.
To make a repellent using pepper, mix black pepper and cayenne pepper, and sprinkle it throughout the garden to keep out dogs. The pepper irritates the dog's nose, but it does not harm it. The irritation helps deter the dog from returning to the area. To keep dogs off furniture, add some cayenne pepper to potpourri and place it near the furniture.
Although both vinegar and ammonia are effective dog repellents, they are dangerous to plant life and detrimental to upholstery. However, HowStuffWorks recommends a method to use these chemicals in the garden. First soak biodegradable coffee filters in either ammonia or vinegar and let them dry. Once dry, cut the filters into toothpick-sized strips and spread throughout the garden to keep out dogs.
Gardening Know How also recommends this method, but with cotton balls instead of coffee filters. They also suggest using alcohol if ammonia or vinegar is unavailable.