BarkNoMore

Do not say anything at all when you spray the barking pup and just calmly walk away.

This is reasonably simple. Get some water in the spray bottle. Stay away from the barking puppy until the puppy barks, then calmly walk to the puppy and spray him in the face with the mist of water.This may seem like a cruel practice but no it is not and it just a water and puppy will learn very fast. Only do this if this is a persistent barking. If puppy just barks once or twice ignore it, it is a dog afterwards. Do not use any electric shockers etc you may ruin the dog.

This is a natural reaction for dogs. The best practice is to release them from the lead and release is going to be associated with the play not an attack mode. In order to avoid the "attack mode" best option is to teach to hill (or stay with me command) and practice often and not to pull back on the lead, because it may trigger the wrong response in the dog.