Ok, this has got to be something I'm doing wrong, since I have had the exact same problem with two completely different dogs. Basically, the issue is that I can potty train my dogs, except for a small area in our basement. Otto started the trend, he was a huge pain to potty train because he has severe crate anxiety, and had pretty bad separation anxiety, though the SA is much better now. Otto is an intact male doxie-pin, about 5 years old (I underestimated when we found him about a year ago, and the vet isn't positive of his age, but that sounds like a good guess). We've had him for just ever a year, and he took almost all of that year to potty train. every time I thought we had it down, he would regress, and we'd be back to square one with the constant supervision and hourly trips outside. I think the biggest issue we had was nighttime, because he CAN NOT be crated with causing himself injury (Chewing on the bars, scratching till his nails bled, etc. It's bad...). But I managed to get him trained all through the day, and he basically picked a spot in the back corner of the basement if he couldn't hold it through the night, and then those nighttime accidents became less and less frequent. The strange this was that for that last stretch, 2 months or so, ever time he had an accident it was in the same spot, in the back corner of the basement. Otto was still working through this, with about an accident every 1-2 weeks, when we got our new dog, Cthullu. Cthullu is a 1 year old fixed male Great Pyrenees. As soon as we brought Cthullu home, Otto was magically potty trained, and other then one time in the past two months when I massively overslept because I was sick, he hasn't had an accident in the house. Cthullu was at square one with the potty training though. He is crated at night, crated when we're at work, and has never had an accident in his crate. He had a few accidents in the house at the beginning, but he seemed to have picked up on it pretty quickly. He goes outside and goes potty on command, he wakes us up in the morning with a few barks when he needs to go out, etc. But he's picked up Otto's old accident spot. If he's loose in the house without eyes on him, he will go potty in that same sticking corning of the basement. I don't get it. If he was just having random accidents, it would be easier to understand. But it's like he thinks it's OK to go down there. He doesn't ask to be let out or anything. If I close the basement door, he will come and whine at me to go outside, or just hold it until I take him outside. But I can't keep the door closed because the cat has to go downstairs for his litterbox, and I can't install a cat door (rental). I have scrubbed that floor, sprayed it with every sort of odor-remover I can think of, and it's concrete so it's not like the smell could soak into the carpet/wood/etc. I'm totally clueless of how to stop this other then preventing him access to the basement, but not only would that be hard with the cat, but it's also the coolest part of the house right now since we don't have AC.