I realize your baby is priority, but the dog is also a member of the family and should never be tied up anywhere, indoors or outdoors.
Rottweilers do not do good left alone especially tied up.
Crate him when you are away. Its a safe haven, and the cat most likely is not going to do anything but act bossy... trust me, I haven't met a dog yet, who was the boss over a cat...
I hope that your wife is in agreement to having the dog, I do not know, so please, if she isn't, and this dog isn't going to be able to be a part of your family, more than being tied up, and left outside, please, do the kindest thing and re-home him.
I mean no disrespect, but only have the dog's best interest at heart here.
