My healthy dog has suddenly started pooping inside the house. Never has before unless he's sick but Ive known he was sick then.?

With dogs, if they have a change in bathroom habits after being successfully house trained, a vet visit should be done so they can verify there is no problems. My sister had a shih tzu years ago that was house trained and she started just peeing right in front of my sister and pooping in her bedroom. My sister didn't take her to the vet and within about 6 months, she found a tumor on her stomach. As it turned out, the dog had mammary cancer. Her vet told her anytime a dog has a change in bathroom habits, they need to be seen by a vet.

I had the exact same problem with my JRT-Chihuahua mix. He was always pooping in the room next to where my cat's litter box was. I take him out 4 times a day and he always poops at least 3x outside daily. I think that he was probably doing it to mark his territory (he was def doing it on purpose) and he was always doing it when I wasn't looking/out of the house. Once I started crating him at night and when I left he hasn't pooped in the house once. Maybe start crating him and see if that helps?

I feel you need to find a way to make time to take the dog out every two hours. The dog then associates outside with 'going'

When there is a big change in behavior like this, take him to his Vet. There is probably a medical issue behind it. Take him in to see a Vet for a wellness exam. Make sure he is utd on shots & stuff. Get a physical, run some blood tests or at least see if he is alright or not & follow the Vets suggestions.

Not the dogs responsibility to let you know when he needs to go out, your responsibility to provide sufficient daily walk/elimination times.

Call your vet for advice, phone calls are free, they may request he be brought in for an exam, bring in a fresh fecal specimen while you're at it.

You just have to reteach him to go outside, just as if he was a little puppy again. Most dogs need to be retaught at least once in their lives.