Owner reports that her 2 y o terrier after having been walked while wearing its harness, bit the husband when he attempted to remove the dog's harness.  

Many dogs, and perhaps in particular, terriers, need to be desensitized to physical handling. When a dog is fearful, reactive, worried, concerned, nervous, anxious about someone fussing about its neck and/or about its body, it will attempt to fight back in the only manner it knows. You see, the dog is attempting to communicate with its squirming.

A desensitization/behavior-modification program has some specific requirements. I believe it's best initially to use a training set-up rather than wait for life to just happen and hope to respond to that.

It's very clear that fear is an emotion. We see the behaviors that arise from fears and anxieties. Many people are attempting to deal with those behaviors. 

As many people in this group have already described, we need to work with the dog at its own comfort level. Some have used the term "sub-threshold."