Regressive Behavior: Sudden Accidents in the House
First and foremost, rule out a medical cause (upset stomach, viral infection, etc.). Next, if you suspect your dog is exhibiting a behavioral regression, ask yourself what context is it happening in. At night or during the day? While someone is home or not? Is the environment unfamiliar? Or is someone new in the house? Identify ALL of the possible X factors first.
A great strategy for any behavioral puzzle is to return to basics. Was he crate-trained as a puppy? How was he confined during initial house-training?
Go back to the ABC’s of training:
Be very consistent with the feeding schedule to better predict when he’ll have bowel movements.
Take him to ONE designated spot to relieve himself, and reward when the job is done.
Try reducing his freedom in the house while these episodes are taking place (gated in the kitchen/laundry/mudroom/etc). Dogs typically won’t mess up a space that's small enough and feels like home.
Once successful, gradually increase the size of his territory and length of freedom until your pup is back on track.
You’re essentially REstating the rules clearly for him.
Even with adult dogs, consider providing a wire crate that he can retreat to, enjoy his meal in or just have some time undisturbed. In other words, the crate is not for punishment but for the security of having his own den (w/ satellite dish, NFL Sunday Ticket or an auto-bone dispenser). Place it in a low-traffic area and respect his desire for space.
It's tempting to assign humanistic qualities to a problem: "He's mad at me/wants revenge/doesn't like my coat/hat/new lover, etc." Truth is, dogs don't have hidden agendas. They simply and earnestly respond to their direct environment. It's up to us to clearly define our expectations.