How to introduce my puppy to my cats

[sspbass]

I have three outdoor cats that are all pretty friendly and one of the especially. 2 of them won't have anything to do with her and the really friendly one is way too trusting for his own good. Our 3.5 month old GSD goes at him like he's dinner and he'll just lay there on his back until she's bit down on something and he doesn't seem to learn. I really like my cats and I don't want to have to restrain my puppy every time were outside. I tried holding her back by her collar to let her sniff him but the second she gets a chance it's like she goes for blood. I think she's only trying to play but doesn't know how much it hurts and she doesn't mouth us near as hard.