This is one of my favorite poems and on one website it was listed as from the Shelter Dog and the author as Evelyn Colbath.

I associate this poem with my dog Tucker who was a stray, then a shelter dog, then had a short failed adoption. The lady was going to take him back to the shelter but knowing we were looking for a dog to adopt, she asked if we would keep him for the weekend to see if we would want him. He tried so hard to fit in that it was only a couple hours later that we knew he was ours. When I first found this poem I would read it to him and then say "Yes, Tucker, FOREVER."