Many adult dogs adopted from animal shelters were housetrained in their previous homes. While at the shelter, however, they may not have gotten enough opportunities to eliminate outside, and consequently, they may have soiled their kennel areas. This tends to weaken their housetraining habits. Additionally, scents and odors from other pets in the new home may stimulate some initial urine marking. Remember that you and your new dog need some time to learn each other’s signals and routines. Even if he was housetrained in his previous home, if you don’t recognize his “bathroom” signal, you might miss his request to go out, causing him to eliminate indoors.
Therefore, for the first few weeks after you bring him home, you should assume your new dog isn’t housetrained and start from scratch. If he was housetrained in his previous home, the re-training process should progress quickly. The process will be much smoother if you take steps to prevent accidents and remind him where he’s supposed to eliminate.