aggressive behavior in our adopted cocker

Question
Hi Kathy, I've had my sweetie pie cocker spaniel for 12 years. He never meets a stranger (dogs or humans), never barks, shares his food, and takes all the pulling and tugging from my five year old without ever snapping. He has always been so good natured...the perfect little lapdog. I know this has a lot to do with having a loving family and a nurturing environment ever since he came to us at 8 weeks.
My problem began yesterday, when I caught word of a pitiful, malnourished cocker spaniel in the local shelter whose days were numbered. I have a big heart and went to pick him up, even knowing his skin allergies would cost me a fortune at the vet. After a thorough examination, vaccinations, medications, and a long bath, I brought him home and realized this little guy was going to be big trouble!
Though he is affectionate,wiggly,loves to snuggle, and follows me into every room, it is obvious he hasn't ever been in a real home before. (He lacks those particular doggy manners) The vet said he was around the age of 6, but he seems younger. He has learned very quickly to potty outside, not to drink from the toilets, and not to dig on the satin comforter, however he is very aggressive when it comes to his "food" and isn't shy about growling, snarling, and even snapping when my other cocker wiggles over to his bowl. Today he nipped at my daughter when she tried to take his tennis ball. The shelter volunteers said he was "great with other dogs and children" but I just can't trust him yet.
This poor guy has had a hard life, I know it will take some time for him to realize he has a home now and doesn't have to be possessive of his food or toys, but do you have any advice for me? I need to teach him how to share! My poor cocker is devastated over our new "addition" and doesn't want to come near him, which makes me feel really guilty. What should I do?

PS: The dogs have different bowls on different sides of the kitchen...the new guy doesn't growl at me when i get near his food, only when my cocker comes within a few feet of him while he is eating.


Answer
Hi Stacey, firstly well done you for taking on this poor little chap, if there were more people like you the country wouldnt be over-run with unwanted dogs, so well done, i actually pick up a little chap myself at easter same age as my girly so we are both gonna be in the same boat.
Your first boy is bound to feel a little pushed out completely understandable someone has come and trod on his territory, however with love and kindness he will hopefully overcome this and the two boys should become best of friends, in the mean time you have a lot of sorting out with the new one, do they get on okay when food isnt involved? or is it just when your new boy is eating.
When you put his food down, make him sit and wait then tell him to eat, stand back and keep your first cocker away let him eat his meal, then as soon as he has finished praise him and pick up his bowl, next step move the new cocker away and feed your first cocker, you could try this for a week or so, after a while whilst your new cocker is eating just brush past him and talk to him let him know you are no threat and not going to take his food, it sounds to me like he has had to fend for himself and is very protective over what he thinks is his, its all about gaining his trust, i know you feel you cant trust him, but i think with time and effort he will be a happy little dog, you obviously have done a great job with your fist cocker and im sure you will crack this one.
When you play with him give the dogs a ball each let him learn from your first cocker that if he gives the ball back to you you will let him play with it again, its not going to be easy i know, and im sure you have the answers in your heart, you will know what to do for the best, im no expert at training dogs with his background but im sure with love kindness bribery and treats you will win in the end.
Im sorry i cant give you all the answers you require, i have asked vets questions myself on behaviour, it may pay you to seek a behavourists advice. I wish you well with your new addition and hope things work out for you. Best Wishes
Kathy