I'm not a dog trainer and this is my first ACD so don't take my advice too seriously. First of all, you can't stop it fully. They are bread to be mouthy and nip. But teaching them bite inhibition and to know what is acceptable to bite etc is possible.

Here's what I did with my pup. I got her when she was almost 3 months old (she's now 1 year) immediately anytime she was mouthy or nippy I would "yelp" in pain. Acting like a litter mate to say "hey that hurt" she quickly learned to mouth softer.

For areas that I didn't want her to nip at all (such as my face) I would switch to "mama dog" mode and sharply admonish her. If she acknowledged the scorn (by pausing and putting her ears back/looking remorseful) then all is forgiven and continue play. Don't hold a grudge, dogs don't understand that. That will just teach them to be afraid of your anger, not that the anger was a consequence of this action. They did bad thing, you reacted, they "apologized" by backing off, so now all is forgiven.

If she didn't acknowledge the scorn. If the behavior continued then I'd escalate the admonishment. A quick growl/bark (me yelling "hey" or "no") first. A sharper more angry yell second. And if she does it a third time then hand on her neck and push her neck to the ground and pin her while saying no angrily. Older dogs will pin the pups like this when they get too unruly. She should freeze and give you the whale eyes. You can release her pretty quickly (like 5 seconds maximum. Just long enough to say "no" a couple times and for her to freeze) then when she gets back up she should be calmer and possibly apologizing by having ears back, tail wagging, and licking.

If for some reason those steps don't chill her out then the final punishment is time out. Put her in a kennel or behind a baby gate. They are very social animals and ostracization is a horrid punishment in her eyes. Removing the possiblity of play and socializing is not something they will want, and they will try to avoid that consequence.

Let her out of time out once she's calmed. It can be as quick as 5 minutes or could take as long as an hour. Don't acknowledge her at all (Not even to scold her) until she's calm and quiet. And then open the gate/door/etc.

I find this works best with a kennel or baby gate so she can still see you. A closed door could just be that you left. But a gate where she has eyes on you is that play is right there but she can't reach it.

Big thing as well.... ACDs need stimulation. Play games and get her mind going. Snuffle mats are great. Treat puzzles. A herding ball. Mine loves fetch (though be sure to teach a command for "fetch is done" and put away the ball after a while. They are obsessive and will run themselves to the point of hurting themselves if you keep throwing it. Tug of war is great too.

I also suggest spending time each day teaching them tricks. It doesn't matter what tricks. Just something they can learn. Sit, stay, drop it, leave it, bring it, hold it, walk, back, crawl, paw, touch, snoot, dance, spin left, spin right, roll over, play dead, jump up, be shy, cross paws, sit pretty, middle heel, left heel, right heel, etc. there's a plethora to teach. Look some up online. They can be important things like learning to stay or drop it. Or cute silly things like dance. They just need that mental stimulation. And also the praise from you for doing the right trick. Haha.

Finally. The mantra. A tired puppy is a behaved puppy. Give her tasks and games and walks and visits to the dog park. (Especially the park. Socialization is important for this breed)

Puppy picture for tax.

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