Since you are house breaking a senior dog, your emphasis should
be on teaching him to eliminate outside, versus teaching it not to
eliminate inside. It is much easier to teach an old dog to do something rather
than teaching it not to do something. If the dog already has an established
history of going inside, it would be harder to target your focus on eliminating
that established habit. It is much easier to teach the dog a better alternative
to an old behavior.
One of the key points while trying to establish this new habit, is to be consistent. To begin, select a spot where you would prefer your dog do its business, such as a particular section or corner of your yard. Even being consistent in the area you would prefer they go is a good technique. Consistently showing the same place to go potty would help the dog learn quicker. It's also helpful if you do not clean the area too often until your dog learns that this is the area you prefer they use.
Be consistent with your voice and choice of words in referring to potty. An older dog might get confused if you use different phrases to mean the same thing. When you want it to go potty, use the exact same phrase to make housebreaking an easier task.
Be diligent in removing and cleaning up every trace of potty accidents inside the home. Their sense of smell is very keen and the smells might confuse the dog in thinking it is the place to go potty. Use a deodorizing cleaning solution to eliminate odors.
Keep your pet's sleeping area as confined as comfortably possible. Dogs do not want to potty in their sleeping area and by using a crate or other confined area, you are eliminating possible space to go potty. Every morning take your dog to the desire potty area to do it's business.
As we do when teaching children, reduce your dog's food and water before bedtime. This can help prevent accidents due to your dog's full bladder while sleeping that may hinder their capacity to control the call of nature.
If possible, make it as easy as you can for your dog to go outside. A doggie door is the best or leaving the back door open. If this is impractical, leave a bell for your dog to reach. Make sure you are consistent with bell training and take the dog out each time it rings the bell so that it can associate being let out and ringing the bell to signal you.
If you are patient and consistent, housebreaking an older dog is not difficult.