Dogs tend to lose their power of hearing, as they age. It is thus a good idea to keep it on leash when going out or stick indoors. Ageing dogs tend to become cranky and thus they snap easily. You should understand that they are not as agile and tolerant as they used to be and that they can bite at slightest provoking. If there are children in house you have to make sure that they do not unnecessarily trouble the dog.
Elderly dogs are very prone to cancer.
If you feel a small lump or protrusion in any part of the body, go see a vet it could be a sign of cancer. Other symptoms include foul odour, unusual discharge or bleeding. Take special care of the mouth, tumours in mouth have a tendency of turning bad. There are some other things that you need to notice and which require immediate medical attention. If your pet is always short of breath do not think that it is because of old age and dwindling energy levels.