Reset the Rewards

If the basics are in place and accidents continue, the reward system has likely gone stale. Outdoor trips that once earned a treat now earn nothing, so the effort of heading out — handling stairs, facing the weather, dropping whatever they were doing — stops paying off.

Fix it by starting over as if the dog were a puppy. Every outdoor elimination earns a high-value treat and real praise, every time, until going out is so worthwhile the dog starts asking for it. This is not backsliding — it is closing a gap that opened the day you stopped rewarding.