It's must less common to teach a dog to use a litter box than it is to teach a cat, but some owners like the flexibility that a litter box allows. If you're in an urban area where it's difficult to take your dog for walks, or if you want to have the option of allowing your big dog to relieve itself on a balcony, deck, concrete patio or even indoors, a litter box might be a good solution. It's easy to build an appropriate box for your large dog, and soon you'll have flexibility when the weather is bad or when you can't spare the time for a walk.
Buy a large tray that is big enough for your big dog to walk onto and squat on comfortably. Cat boxes are usually too small for this purpose. Choose a plastic or metal tray, which will be easier to clean and reuse than wood. Metal is preferable because it won't retain odours. The tray should be deep enough to allow you to fill it with litter and to place synthetic grass on top if necessary.
Fill the tray with litter. You can use either regular cat litter or a brand like Second Nature that is made specifically for dogs. For big dogs, you should choose a deodorising brand, especially if the dog uses the litter box indoors.
Attempt to teach your big dog to use the litter box outside before you begin indoor or patio training. Adult dogs that have learnt to do their business outside may have difficulty learning to use a litter box if you try to teach them to use it in the new area immediately. Place the box in your big dog's usual potty area, and place some of its previous "mess" in the box to encourage use. If the dog won't use the litter box, add a layer of artificial grass on top.
When the dog is comfortable with the litter box and is using it consistently outdoors in its usual potty area, shift the box into your home or in the area where you'll keep it permanently. Instead of taking your dog outside at the typical times, put it out onto the patio or balcony or confine it in the area where the litter box is located. Praise the dog when it uses the box.
Clean the litter box immediately after each use. Even if you use deodorising litter, big dogs can generate unpleasant smells, especially inside a house. Remove the waste as needed, and the entire box should be scrubbed and filled with fresh litter twice a week. You can easily make a new box if needed by simply replacing the tray, and if you're using synthetic grass, replace that when it begins to wear out or retain odours.