It should be pretty obvious why you need to house-train your dog, and if it isn't, well, we can't make that dinner party next week after all. But if you want to get your dog to stop peeing and pooping on the rug, read on.
There are several reasons why an adult dog might suddenly revert to soiling in the house. The cause may be medical, hormonal, managemental, or behavioral. The first order of business is to get your dog to a veterinarian. If the veterinarian can't find anything physically wrong with your dog, the problem probably has something to do with mismanagement or the dog's emotions.
The first step in re-training acceptable toilet habits is to observe your dog carefully in an attempt to establish a pattern to his/her behavior. Keep a diary of when and where accidents happen. Are you at home or away when the accidents occur? Also, keep a list of when your dog goes outside and what you were doing at the time. If you find a pattern to the behavior, for example, your dog seems to be going in the house only when you're away for a long time, make sure you take him for a good walk before you go out and try not to leave him alone so often or for so long.
House-training an adult dog isn't much different from house-training a puppy - in fact, your adult dog should be able to “hold it” for much longer than a puppy, making retraining an adult less labor intense. Dog crates can be useful training tools when it comes to correcting house soiling problems, because dogs generally will not soil in their immediate environment. However, if your dog has never been placed in a crate, take care to introduce him slowly. For some dogs that are crate phobic or have been forced to soil in them in the past, crates will just not work.
Also, consider that your dog may define “home” differently than you do. To you, home may be a multi-story house, but your dog may see everything beyond the kitchen (which he has kept spotless) as “outside.” By restricting your dog to a smaller area for a while, and then gradually extending his home area, you can help him learn the ropes.
The procedure: Take your dog outside, on leash, to a regular “toilet area” and give him a food treat for eliminating there. Try to keep “toileting” walks brief: If he's going to urinate, it'll probably happen right away. If you do not have immediate success with him, take him for a longer walk, try using a different leash, or try exiting from a different doorway. This way you can emphasize that a bathroom walk has only one purpose. If he doesn't cooperate in time allowed, return indoors and supervise or restrict him, then repeat the bathroom walk in 15 to 30 minutes.
If you discover an “accident” after the fact, clean it up without a fuss - punishment today won't stop the behavior from being repeated tomorrow. Usually, consistent supervision or confinement and regularly scheduled bathroom walks (don't forget the rewards!) will eventually teach your dog what is expected of him. If you catch him in the act, tell him “no,” but resist the urge to shout. Instead, reward him lavishly when he goes where he's supposed to.
Editor's note: In addition to the above measures, it is imperative to thoroughly clean up previous messes. Physical clean-up and/or attempting to mask the odor will not do. Instead, a proprietary odor neutralizer should be employed. These products contain enzymes or live bacteria that destroy odors at source by breaking down the molecules. Some effective products are: Nature's Miracle, Anti-Icky-Poo, Odoban, Odonil, Nilodor, and Eliminodor. Make sure the product is fresh and is used in accord with the manufacturer's directions. Without this step, the dog will be attracted back to a previously soiled area like a heat-seeking missile to a source of heat!