Unfortunately, if you can't convince your parents, I don't think there's much you can do other than spread the word that he's available to other ferret lovers who may be looking. Too bad, he seems like such a sweet guy, and I know how frustrating it can be when your parents won't allow you to have the pet you want (I wanted ferrets for so many years and my mom was totally against it. Eventually I got them when I moved out, but now I realize that was ideal, considering she would have complained about them being out of the cage, accidents on the floors, ect and they wouldn't have had as good a life). Just be happy you have the rats, some people aren't even that lucky
