It is entirely possible that Pixel isn't completely house trained, but we have him on a schedule that allows him to get outside when he needs to. We don't have issues in the level of the house where we spend most of our time, but until recently Pixel wasn't allowed downstairs where the bedrooms are because that was the cat's area.
The first few times he slipped downstairs and peed or pooped I thought maybe he figured since he wasn't in that area very often he was confused. Plus the carpet reeks of cat so it's an easy mistake I guess. Recently he got downstairs and was there for less than 2 minutes and he'd already peed/marked and pooped in the storage area.
I've noticed that he is less likely to empty out in the carpeted area now that he gets to go downstairs to sleep with me, but if the storage room door is open so is the restroom.
Not only is this gross and annoying, but we're moving to a new house at some point. I'd like to let the dogs have full run of the house from basement playroom to second floor bedrooms, but I don't know how best to stop this. Obviously I won't let him have run of the house until he's proven he can be trusted in smaller areas like a puppy, but my kids can't keep gates closed to save their lives.