My partner was badly bitten after patting our larger dog on the bet. What can we do?

We have three dogs--to small terrier mixes (Gina and Henry, both over 12 years old, both about 15 lbs.) and a larger brown hound dog, Willie, who is about 60 lbs. We were told he was a lab/German Shepherd mix when we got him at the SPCA, about 7 years ago, but he is clearly some kind of hound. When we first brought Willie home, he was smaller than the terriers. Willie was quite aggressive with the terriers (causing several vet visits) as soon as he was physically bigger than they were, and he's bitten me a couple of times, once because I unwisely got involved in a fight among the dogs, and on another occasion because I reached my hand in the general direction of one of his bones. We engaged an animal behaviorist who helped us work with Willie and the other two dogs to get the family dominance hierarchy clarified for everyone. At the time the behaviorist suggested that we were really not giving Willie a chance to be a good dog, by undermining his rightful place as the dominant dog among the three (we had mistakenly tried to treat the dogs all equally), and by not making it clear to him that we were in charge. We undertook a bunch of changes--like us eating first, making all three dogs work for whatever positive things came their way, and supporting Willie's rise to the top of the dog hierarchy. We also started leaving him on a leash basically all the time so that if something happens he can be restrained. Things improved greatly and the dogs appeared to have worked out a nice peaceful coexistence (and we, probably unfortunately, relaxed a lot of our rules). Then we moved from Texas to Missouri and things are back to a bit crazy. One problem is that Willie has developed some serious separation issues--barking at us and trying to escape out the door when we leave for work in the morning. He has not acted aggressively against the two little dogs, but he has shown some unusual growling and nastiness. Also he is much more "needy" and constantly begging for affection and attention. He just doesn't seem like he can relax. Last night was the worst aggression we've ever seen from him. In the middle of the night, my partner had gotten up to take one of the little dogs outside and Willie had moved up to her spot on the bed. When she returned to bed, she reached out to stroke his head and tell him to move and he started to wildly bite her arm, in a frenzy. He gave her about 6 deep puncture wounds and some serious bruising. He stopped as soon as the lights were turned on. We immediately isolated him in a basement bathroom. Now we are trying to understand what happened, if it can be prevented, or if Willie has finally crossed the line. He has never attacked my partner before (she has been his strongest supporter). Again, though, he was fast asleep and I know that some gentle dogs may act aggressively when wakened from sleep. Typically, she would not have stroked his head like that--typically she commands him in a clear voice "Off Willie, Off" and he moves. Do you think it is wise to treat this as a slip up and try to reinstate the treatments that worked before or should we consider something more serious? Any advice would be greatly appreciated.

Laura