Have you looked thoroughly into your local dog ordinances? Seems to me you are not obligated to give him back. In my area there are very strict negligent and animal cruelty laws. I have taken in strays and re homed them, cats mostly, but one time an especially large dog I didn't have enough room for. People should be ashamed of themselves. Dogs are not expendable. Sorry, a soapbox of mine at the moment. Long story.