I agree with Kay. I don't believe there are many *valid* reasons to rehome a dog. Of course, you can always rehome a dog to a better home, but, like you said, there will always be a better home than the one before. However, that's like trying to find perfection, which is like a glass ceiling, IMO.

Giselle would love a home with multiple greyhounds, miles of jogging, and daily visits to the dogpark, but I can't possibly provide that. Is it to her benefit to rehome her? Possibly. But the home who takes her in will most likely be unable to give a home to a much needier pup. I personally don't think that that's ethical. As long as the dog is happy, healthy, and well taken care of, I don't see a reason for rehoming.

In the case of the obedience dog who turned herding dog, I'm not sure if I would agree with that. It's clear that the dog loves herding, but I'm sure the dog would love companionship much more. This is why I don't agree with some breeders who purchase a dog in hopes of showing it and then rehoming it when they realize it can't be shown. Dogs are our lifetime responsibilities. Not breeding machines. Not obedience machines. They're ours for life. We owe it to them to provide love and stability.