
I think that maybe a female as well, because if you get another male they may well fight when your bitch comes into season, but on saying that if you have another female then your male dog will be stressed more often, are you keeping up here I think I'm loosing myself :)
Maybe you should consider having your current dogs spayed or neutured (although lots of people don't agree with this) if you have not already done so, then introducing a new pup should be easier. Bitches can fight as much as dogs, I have too bitches that will not share the same run, although they are ok in the car. Still I would still be inclined to go for a female as long as you have good safeguards from your male when they come into season.
Please join, we would love you aboard :)
Kerry