Find a dog Behaviorist. I’d be leery of a trainer that recommended you return the dog. Perhaps she isn’t qualified enough to help you with his problem.
Look in the yellow pages for area veterinarian offices. Call them and ask if they can refer you to a dog Behaviorist.
When you interview the Behaviorists, they should be kind, confident,knowledgeable and give you a good overall feeling about the task ahead.