Tank, the chocolate-red chihuahua, was adopted from a shelter where he was brought after a raid on a puppymill that netted 82 little dogs. Tank was estimated to be four or five years old and had probably spent his life in the filthy puppy mill.
As a dog who spent his whole life in stud service, he got along well with female dogs, but had never otherwise been much socialized. He was nearly a wild animal.
He got along swell with fawn-colored Angel, the three year old female who the adoptive dog owners already had. But apart from mom in his new family, with whom Tank quickly bonded intensely, Tank did not like anyone, and constantly lunged, barked, and bit at anyone else who got near him.
The family was patient with Tank to get him to feel safer and more trusting, but this is a typical example of why thirty to fourty percent of dog adoptions don't take, troublesome dogs being first to be returned to shelters.