Training a dog can not be done if the dog is over threshold. Threshold levels are different for every dog. Once the dog is over threshold it needs to be removed from the stimulus. Giving a leash correction while the dog is over threshold can add aggression or fear towards the stimulus. If the dog stops barking, can you say for certain that he is below threshold?
The key is to keep a dog below threshold and slowly adding the stimulus and rewarding the dog for staying below threshold. Dog handlers, trainer, owners must learn to read their dogs and reward the correct behavior.