Rescue pup - escalating biting

We adopted a 16-week-old Australian Shepherd pup who had been surrendered by a family who got him from a breeder at 10 weeks. They had a 3-year-old and 7-year-old sons. I am assuming the pup became too much with these young children as well.

Reggie is a very loving dog with a fun personality. My husband and I are older but active and we get him the exercise I think he needs with daily hikes. We also have cows and plan to teach him to herd when he is older. Our 20 and 21-year-old children are home now and have also exercised him.

My issue is that Reggie is a biter, not just a nipper at your heels. He originally would mistakenly nip at you during play but now I think that he is becoming aggressive almost as a form of play. When I walk him, sometimes he bites the leash and if I stop him he jumps up and bites me—my arm or hand. To stop him, my trainer has told me to make him sit and refocus him on me and then reward him with a treat or praise. I feel like I am rewarding bad behavior.

If you are walking him and you run with him he does the same thing. He literally jumps on you biting and I have had to hold him down in this overexcited state. He also seems to provoke you if you are sitting by nipping at you to get you to chase him.

I am at the point where I am putting him in the crate for this. I know that is not the right response but I am at a loss. I love this dog already but his behavior is escalating. He had been progressing well but over the holidays my sister visited with a young pup and his behavior has gone downhill since they left. Help!

We have had a Rottweiler and a Rottie/Border Collie mix and I have never encountered this behavior. Not sure what is the right thing to do.

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