
Hi,
As both your dog and bitch have been neutered you can rule out hormonal marking, so no need to worry on that score (as long as your bitch's spaying was one of the rare occurrences of incomplete removal).
I feel the length of time that he is crated could have a bearing on this. If he is crated most of the day and all night as well, it's quite possible that he still feels like a 'visitor' in his own home, because his scent is in limited areas. If he were mine I would have him out of the crate during the day (unless I popped out shopping for an hour or so) and had him around the house with whoever's home. Go back to basics and train him like you would a new puppy - out every half-hour or so. You have the advantage that he is old enough to be taken out for walks as well! And let him have more run of the house with you so that it smells (to him) like his home, and not that of a stranger.
Good luck.
:)