Greyt advice by all but I just wanted to add to the whole greyhound thing: most American greyhounds owners are vehemently against letting their dogs off-lead in unfenced areas. We've seen FAR too many cases of lost/hurt/killed dogs. Trust is a very deadly disease. When people say their greys have solid recalls, I invite them to let their dogs lure course, wait 5 seconds (since that it usually one's reaction time), and recall their dogs. I would eat my arm if the dog came back.

On that note, I would also like to add that many English greyhound owners routinely let their dogs off-lead. I assume it's a regional thing. And FWIW, I walk my other dog off lead. It's a matter of training, breed characteristics, and the environment itself.