Ooh, I wouldn't have thought of a Tibetan Spaniel, until Ashley mentioned it, but it is a great guess. It would explain the ears and the tail. As a matter of fact, a friend of mine had a Tibetan Spaniel and another dog that is a Jack Russell Terrier/Lhasa Apso mix. If you combined those two dogs I think you would have a dog that looks very similar to your dog. Although with the length, part dachshund (as Ashley said) is also a very good guess, and the coloring could come from a doxie also.