An older dog mite keep the pup in check, if they are trained [bANNED TEXT] there shouldn't be any nastyness. I start the pup off with ferrets at around 4- 5 months so the dog can grow up with the ferrets just in the garden at 1st. i find a pup will always learn off older well trained dogs may be just watching for the first couple of times on a lead. just a few thoughts. a beddy x whippet or that with a greyhound in it, a pure whippet will also be good choice