Please get that dog to the vet and get that tooth checked. If he has a bad tooth...that is usually VERY painful. If he has to go under an anesthetic have the "other" end taken care of as well (neuter him). The aggression HAS to be dealt with. Hopefully the behaviorist can help you.
Cindy

Thanks for all the posts! I really appreciate the feedback.
From today on, Ally and I will "tag"team him and hope that he gets it! Do I use the muzzle,too? Does this mean that nobody else gives him food or water,ever? What about the other 2 kids- I haven't let anyone but my husband (he sometimes has to) - can they walk w/Ally or me?
Tomorrow AM I'll call the vet to recheck Willie's tooth,ASAP or maybe just remove it. Also,neuter him because my vet recommended it when he went for his initial check(probably the only time he had ever seen a vet.
Sorry if I've taken too much space but I really want to do what I can to save Willie.

Eileen
I think it would be a good idea to use the muzzle on him, that way if someone messes up he can't bite. It will re-inforce his bottom of the pack position, and Ally will be more confident around him.
It would probably be a good idea to get all the rest of the family walking in front of the muzzled Willie too.
I agree about getting his tooth checked or pulled, that would sure make me cranky, but I don't think we can blame all of his faults on the tooth.
Good for you for making the effort and doing the research to reform your dog!

Thanks for the correction. I should clarify that I do agree that a child should not be doing any domination work even if it is supervised. Especially when the source of the problem has not been identified. Sorry about that one! Don't need anyone getting hurt. Have a good one.

Thanks. Talked w/ the vet and Willie is going in Thursday to extract the tooth and get neutered.Although he doesn't really know Willie the vet thinks we can tain him and will help us.
Again- thanks to all of you who took the time and are concerned enough to respond to my problem... desperation(?) I am ordering Ed's books, am spending too much time online listening to the podcasts(maybe Ally will lend me her IPod?)and rsading everything I can.Also using recommended techniques & stategies. Ally isn't crazy about being near Willie but she says she's not afraid- just mad at him so we'll walk his little legs off.
I'll write back after his surgeries.

Hi Eileen, please do update us on Willie's progress, and yours, too. I've been reading this thread, don't really have any advice that hasn't already been given. VERY glad you are getting his tooth taken care of.

Thanks, Jennie & Janice.
Here it goes, again! I will talk w/the vet re.cancer, infection risk. Ever feel like no matter what you do it's wrong? (not to mention what my husband will say about the bill).

Sounds like to me you are doing everything right to the best of your ability.
And I applaud you for taking in a rescue. I work in rescue so I know how trying it can be to re-train a dog with previously learned bad habits.
The best thing is getting your dog's tooth taken care of. As someone who has suffered cracked and abcessed teeth myself, I can feel for the poor dog. A sore tooth can put anyone in a bad mood.
Then you can start with the re-training. To neuter or not to neuter is really your own decision to make.
Your daughter needs to learn not to be mad at the dog. You can't help to train, even with no contact, if you are angry with the animal. It's counter-productive.
The muzzle is a very good idea while Willie is learning his new place in the pack.
Keep in mind, this dog has a lot of terrier in him. Terrier's tend to want to be bossy and are very determined little dogs in general.

Hi, Janice. Your empathy helps.I would have had the tooth out ASAP if either the vet or I had thought it was painful- it isn't broken or abcessed per his exam: he had said "sometime within the year". I think it might be painful because the only time he threatened me was when he had been chewing on a corncob- by the way, is that OK? Re. Willie being a terrior mix, I expected him to be high energy and assumed that he was a dominant dog because he was confident and made it clear to our Lab/husky that he was in charge. I not only kept Willie and Harrison apart, but also other dogs because I wanted to prevent anything from happening. The people who had him basically ignored him so I knew that he wasn't going to be w/o problems but I honestly don't think that I totally blew it by missing a lot of signs- I was always wary w/ him because he was new to us but he never growled, raised his hackles,etc. until the first incident w/ Ally.
I hope it doesn't sound like I'm making excuses for either of us. I guess I'm just insecure about the outcome for Willie and I want to go back to the pre-aggressive days when he was so good within our family (except w/the cats). I'm not sure that I/we are eqipped to handle this -and I worry that either I'll be faced w/ giving him away or worse. And if he went to a new home I will worry that if he should ever hurt anyone that it would lead back to me... if Willie ever bit again I would feel responsible because I didn't have the heart to put him down and took the easy out.