What is the best approach to correcting a terrier who insists on "protecting me" from my husband?

The dog has been left with the impression that you want the dog to take the leadership role in the relationship. Leaving the impression that it's the boss. Take the time to learn as much as you can on an on going basis to learn dog psychology. This will enable you to communicate with the dog under any circumstances. You would be amazed at the things that will show the dog that they do not need to be the one to control the situation. So many people think of them as human and treat them as such. This is what is actually causing the behavioral problems. Things such as having control over the food, not letting them out the door ahead of you. Providing basic rules boundaries and limitations will relieve the dog of the overwhelming stress and indication that they have to be in control of the situation. Dog's only take a leadership position out of stress because there is no clear leader in the pack.

This is how I would approach this issue:

To start with, I would not allow the dog in the bedroom, bathroom, loft, and other areas where the aggressive behavior occurs. After a while, the dog can enter those areas upon invitation only. Reward him with something that you know he really values when he acts in a desirable manner (i.e. shows no aggression toward your husband). The reward can be a treat, attention, or his favorite toy, for example.

As soon as he exhibits aggressive behavior toward your husband, you walk out of the room and ignore the dog completely. Return only after he stops the aggressive behavior. After a few rounds of this he will likely understand that bad behavior will result in you, not your husband, leaving. In other words, he will not get the outcome he is hoping for, but rather the opposite.

If you are not already, I strongly recommend to have him work for all valuable resources - food, toys, playtime, and anything else he enjoys. Reward him with these only when he is behaving well. Have him sit for his meals, when handing him a toy, and any other time when he wants something. Once he sits give him his food/toy/attention/treat along with verbal praise.

Once he realizes that he can get what he wants by following the rules he will look to you for guidance in most situations, knowing that by playing by the rules he will get what he wants (most of the time).

I hope this answer gave you some ideas on how to deal with this issue. If you feel like nothing is working it's always a good idea to consult with a trainer.

Good luck!

Years ago, my family had an issue with a dog who was defensive/anxiety ridden, and nipped my brother. Dog’s rely on humans for care and their basic needs, including food (which dogs typically are very motivated by. A possible solution would be to make your husband responsible for all servings of meals for your dog, so then the dog must learn to rely on and respect your husband for the sake of receiving food. If your dog acts aggressively while your husband is dishing out food, have him turn around and completely ignore your dog’s tantrum, which then also will delay the dog receiving the food. Over time, your dog will learn that association that receiving food will be delayed by aggressive behaviors, and conversely will be rewarded by food in the absence of aggressive behavior. Hope this helps!