Hi there im training to be a behaviourist at the moment, you need to get the puppy right in there early stages, the critical peroind of development in a puppy is from 7 weeks to 12 weeks, if this was my dog i would stand back and see when the behavoiur triggers, but you seem to no when this is i would not put the dog in the situation were it is going to explode in to panic and biting.

I would build a real good leadership up with my dog so the dog trusts and sees me as leader so when he sees another dog he is quite happy for me to deal with the situation rather than to poor mite trying to take the whole world in to his own hands, i would also find a really wow treat that he loves or a toy he gets only when out on walks and get is distraction of the other dogs and on you, i would keep on the lead for the time been, but dogs on leads can also lunge out as they feel more threatened when passing a dog try and keep the lead as slack as you can if you put tension on the lead your telling your dog there is somthing wrong, if this happens again when he sees a dog turn away and walk the other way never put him that situation which will make him scared only walk passed when you can see he is calm then praise him good luck keep us posted

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