A number of household products can be used to prevent your dog from doing its "business" on your deck. Before treating the area, you need to scrub it clean first. Use laundry detergent and water, and add a teaspoon of baking soda to remove the odor. After it dries, apply a homemade repellent to the deck to discourage the dog from marking the area again.
Sprinkle cayenne pepper, black pepper or powdered chili in the dog's favorite toilet areas on your deck. Use the spice in moderate quantities as it will irritate the dog's nose when it sniffs it. Be careful not to use too much or it could cause inflammation in the dog's nostrils. Alternatively, dilute the spice in water and apply it with a spray bottle.
Vinegar and Lemon
Mix a solution of vinegar and lemon juice and spray it on the deck, or soak cotton balls with the mixture and place them in strategic spots around the deck. The strong scent will repel the dog and will also mask any old urine odor that draws it to the deck. However, the sour smell on the deck may be too strong for you to tolerate.
Ammonia and Alcohol
Ammonia and rubbing alcohol are strong-smelling substances that your dog will not enjoy. Spray them around the deck or use soaked cotton balls to distribute the aroma. Reapply regularly to maintain the smell.
Wipe essential oils, such as eucalyptus and citronella, onto the surface of the deck, ensuring that you do not make the floor surface slippery. Both have strong scents and will mask previous smells so the dog will have no reason to urinate there. An added benefit of eucalyptus is that it repels fleas, and citronella is known for its mosquito-repellent properties.
Dry out used coffee grounds in your oven and place them in the corners and other parts of the deck. Dogs dislike the bitter smell of coffee and will avoid the area.
Most dogs are unlikely to urinate near their food and drink or sleeping quarters. Leave a bowl of water on the deck for the dog to drink; this may discourage it from doing its business in the same area.
Some commercial products are available that make use of natural plant oils and are described as "liquid fences." These also mask previous odors, causing the dog to feel less comfortable about urinating in the area. The products are biodegradable and can be used safely on plants and around your dog. The effect will last up to a week after which the product will have to be reapplied.