What causes dog to start urinating in house after being house trained for years?

When a trained and well-behaved dog suddenly starts peeing around the house, you have to consider that something has changed. Usually, the problem of sudden onset of dogs peeing in the house may have two causes which are categorized as follows.

1. A medical reason. It is essential to first rule out what could be the present and possible medical condition of your dog. It could be a urinary tract infection, bladder disease, diabetes, kidney diseases, arthritis and others.

2. A change in behavior brought out by some other external factors. This could include a new pet in the household, a new baby, death in the family, separation anxiety and so on.