When we have a long bout of rain our dogs hate going out in the wet so they sneak off to corners and go there. Then if they aren’t caught in the act they figure they got away with it and repeat the act. I have used baby gates to make those spots unavailable, plus I force the dogs outside rain or no rain about every two hours, and I fuss at them (No! Bad Dog!) when I catch them in the act. It helps get them back to their training.
The trainer we work with says that what they do is keep the dog outside for a full 24 hours, feeding it outside, letting it sleep outside, and so on, and then reintroduce it to the house. If the behavior recurs, out the dog goes again. Dogs quickly learn that if they “go” outside rather than in, they get to be back in the “den” again. We can’t do that because we have a neighbor that refuses to tolerate any barking of any kind. I would talk to them about it but I don’t know who it is because they communicate by means of anonymous letters.
Has anything changed in your (and your dog’s) life recently? Are you working different hours? Do you have a new pet, or a new addition to the household? A new love interest? Even a new hobby that takes your attention away from the dog? It sounds as if your dog may be feeling insecure and reverting to puppy behaviors.