Dog Training/potty training
I have 2 dogs one Shitzu about 14 and the other 1/2 alpso and 1/2 something else she's about 16.
Both pee in the house - started about 3 years ago - not every day but on and off - both go outside a lot fenced yard.
2 spots they pee - 1 in basement on wall to wall carpet and the other on 1 corner of dining room rug (which I just cleaned and pulled up. Last night after the rug had been gone for a few days 1 one them (I think the shitzu) pooped in the 'exact' spot they used to pee in (when the rug was there) nows its a hard wood floor - I can not tell you the amt of money I have spent on "dog scent eliminator" wash - spray etc etc - I have dog underpants for the little one (shitzu) but she gets them off at night... as I said its not every night but to often for these dogs who have lots of opportunity to be outside and do their business there.
It sounds like despite the cleaning the dogs are still smelling "potty" in the areas they've gone before. I usually recommend Nature's Miracle. You'll want to soak the carpet right down to the padding before blotting up. A black light can help you see if you've missed anything. For the hardwood, let's hope it hasn't sunk into the wood over the years. There's no easy solution if it has, the wood would have to be replaced. Probably easier to block the dogs from that room. When you are not home, are the dogs confined? A crate or baby gate would prevent them from wandering and pottying when you aren't there to interrupt.
When they go out, go with them to make sure they are emptying and not just enjoying the yard.
Last note: with their ages it's possible that there is some age-related incontinence happening. That's a very normal thing for our senior pups to have. If you haven't already, a trip to the vet to check things out might be the answer.