Ree, I feel really odd answering this question, I know how much more experience you have with Akitas than I do, I almost feel that I dont have the right to say a thing.
To me, it sounds like he may see himself as in a higher authority in the pack than you, he may not be domonstrating this in all the ways he can but keeping this authority for situations like this. Its my understanding, in a dog pack situation, the alpha dog is the main protector of its pack, and if Alpha is not around, the next in line takes over, Is it possible that this is why he kicks into protection mode when hubby is out?
Kato behaved in a similar way for a little while not that long ago, if there was a knock at the door he would be first there barking and carrying on. and would growl at anyone he hadnt met before coming in.
We now when visitors (particuarly people Kato does not know) put him out the back yard but leave the main door open and only close fly screen, as a family would then greet the visitors, where kato could see us allowing them in home, but could not access the situation and control it his way, if he made a scene we would close the main door blocking his view of what was going on, and then a few moments later open it once he settled, bringing visitors further into the house, and letting him see us clearly, welcoming by hugging and touching visitors........
It has got to the point now, in 90 percent of the cases, that he allowes us first to the door, he stands behind us now, and is the last to be allowed to greet guests, known to him or not.
Just a thought and suggestion anyway, i could be wrong, but I do truly wonder if it is his way of telling you that he is alpha to you, and in so being, must step up to the role of protector when hubby is not there.
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"The purity of a person's heart can be quickly measured by how they regard animals" | 
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