Not all owners have the time and knowledge to train their dogs. Some people may not find it very worthwhile because the dog is too old for the sort. The end result is nothing life threatening, but giving the dog proper training in physical, mental, and emotional aspects are rewarding and can even improve the relationship between you and your dog. Perseverance is what counts the most when it comes to training any dog no matter the breed. However, if the dog is aging, some modifications need to be made on the actual training if you want to add a few years to his lifespan.
It is never too late to properly teach an older dog how to potty as long as his eating habits are still good. It may be more difficult with certain breeds, but several tips can be applied to make the process a bit easier. When it comes to teaching potty habits or any other habits for that matter, focus on the things that your dog should do rather than the habits that your dog should avoid. Consistently encouraging new habits will overwrite the bad ones in due time.
Like regular potty training, find a good outdoor spot that is accessible so your dog can repeatedly head there when he needs to go. For the first few weeks, do not clean that area so the dog's sense of smell can cause him to head there. On the other side, keep all of the other areas clean so he will avoid those spots. You should keep his sleeping area clean as well. With some consistency your dog should be good to go and obedient enough for other forms of indoor training.
Indoor training is fairly difficult compared to younger dogs because it may take some time to truly understand their surroundings. With the potty concerns out of the way, your dog may be more responsive with the rest of the training.
The trick is to make the dog realize what areas he may stay in and what areas he may not stay in. As long as you keep those specific living areas clean and open-spaced, your dog will learn to stay in those areas like any household pet. Some days with your indoor dog may not go as smoothly as other days. Some old bad habits may surface and you should respond accordingly using a calm tone. There is a chance that your dog may not listen to you and continue minding his own business. Do not increase the pressure and keep the tone consistent saying "No" when he does something bad. If accidents occur, simply say "No" again and clean up the mess immediately.
Similar to potty training, teach good habits whenever possible and reward your dog when he finally does something right. Behavioral patterns should change over time after a few weeks. Try to stick with these two areas first because other forms of training may confuse the dog. You can get him involved in more energetic activities as soon as he knows how roam around your house like a young dog.