My 5-month-old dog is fine with my daughter's dog and a friends dog, but when I take him to obedience classes or introduce new dogs, he gets aggressive. How can I correct this?
You can try to "down" him as soon as the strange dog approaches to be introduced. Give him a treat at the same time. This is not going to be a fast fix, but your puppy is probably nervous about the new dogs and is fear biting, not being aggressive.