lovely dog turned monstrous!

Question
hi there!
i've recently rehomed a 6month old terrier cross, not sure what terriers are in him as he has coarse yet fluffy red fur and chihuahua like ears and is nicknamed 'foxy' for a good reason! he was living with 9other dogs and9 cats with his foster mother who had hand-reared him from 2days old as his mother was a stray and at 8months old died herself shortly after birth. he was also found on a rubbish tip so either was a stray or had been abanoned along with his mother, it's all uncertain.well he has been living with us for 2 months now and since he was neutered at 7months he has become impossible! he is lovely towards humans and loves attention ad playing soccer but lately he is very vocal towards other dogs and nipped a golden retriever on the tail when off the leash in the park the other day. he suffers from separation anxiety bigtime and cannot be left alone for 5minutes without defecating and running around spreading it everywhere. he sleeps in his own bed beside mine but is put in the kitchen whenever the house is empty, usually about 2 hours a day, and will not be quiet until someone is home.i don't know what to do about his recent aggression. he is brilliant at recall when off the leash (my lab was terrible, would stroll in 3hours later) and will come back the minute he is called, and if he doesnt and i turn around to walk away he will come running which i am unsure if i should encourage as i'm scared this will reinforce his separation anxiety! could his aggression have started as a result of being bitten (not serious but scary enough) by another dog roughly the same size? and if so why is happy as anything playing with molly who is roughly the same age as him and they can just be puppies together and have a ball,and some other dogs! he is worse when he is on the leash aswell, much more vocal! i really don't know what to do about him as he was so friendly and loving towards anything and everything, even my rats, until about a month ago. he would just lay on the beach and not bother with the other dogs but now he's  little demon (albeit a beatiful one :P) and i don't know what to do with him and how to do it!
please help! any input would be greatly appreciated as i really don't want to have to take him back to his foster mum so he can be dog number 10!

Answer
Naomi -

He sounds like a handful !

He's also at an age when he is starting to feel full of himself and starting to really think he's a tough guy.  It's hard for little dogs to be "macho" since they have to make a big show of it to get anyone to believe it.

And without really know what is in him, you should work from an assumption that he is one of the more nervous small breed mixes - like Chi's, rat terriers, etc.  They have a much harder time managing their anxiety than one of the true terriers (cairns, westies, borders, etc) because they are essentially a toy breed.

the separation anxiety makes a lot of sense with that perspective

His barking on the leash is a form of resource guarding - with YOU as the resource.  If you don't get him to stop this now, it may escalate to aggression when he's on the leash.

In the immediate term, I would work on crate training (Make sure the crate is only a little bit bigger than him since they will mess their crate if it is too big), and what is called "Nothing in Life is Free".

Usually people think of that technique for dogs who are too assertive, but I also find that it helps calm over excited or anxious dogs as well.  Here's a link to an excellent description and set of instructions:

http://www.cairnrescue.com/docs/NILIF.pdf

While you work on this, get thee to an obedience class right away....  This technique can help you get a grip on the situation immediately, but you need some guidance from someone who can actually see the behaviors.

It is an excellent use of time and money and helps set you up for a lifetime of enjoying your little monster rather than always worrying about what will happen next.

Good luck

-Beth