Older German Shepherd Who Doesn't Know He's Pooping
When a dog passes stool without seeming to notice, the cause is usually a problem with the nerves that control the anal sphincter, or with the anus itself. It's different from a dog with dementia, who may forget house training but still knows he's going.
In an older German Shepherd, one of the most important causes to check for is degenerative myelopathy. It usually starts around 9 years of age with scuffing or wobbly back legs, and in the later stages it affects bladder and bowel control. Lumbosacral disease (narrowing at the base of the spine), disc disease, spinal tumors and anal sac problems are other possibilities.
Your vet will do a rectal and neurological exam and may suggest spinal imaging. A genetic test can show whether a dog is at risk of degenerative myelopathy. In the meantime, take him out often, especially right after meals, put washable pads on his bed, and keep his back end clean and dry.
See bowel accidents in older dogs and degenerative myelopathy.
This is general information, not a diagnosis. Please follow your own vet's advice.