I agree with K&P, if you punish a dog for giving a warning that it is uncomfortable - it will just learn to suppress the warning and go directly to biting. Warnings are good - they alert you and give you a chance to protect your dog from the situation that upsets it.
The "Look at That" (LAT) technique as described by Lesley McDevitt in "Control Unleashed" is for training reactive dogs to be calm... and it involves working with the dog where it can still pay attention to you - not when it's completely over the top out of control - so you might need to start at a big distance to the distraction (thing the dog reacts to). Then you reward the dog for looking at the distraction. This may seem counter intuitive but it changes the meaning of the distraction for the dog. Turns it into a fun game instead of something to be anxious or upset or predatory about. Reward so that the dog is looking at you then say "look at that", when the dog looks at their trigger/distraction, say "yes" (or click) - most dogs familiar with clicker training for anything else will look to you for the treat - reward while the dog is looking at you. If the dog can't look at you, the dog is too close, increase your distance. Do five minutes of this, and a very high rate of treats. Eg 18 tiny treats a minute is about right. Practice every day if you can. For me - the lawn mower man doesn't show up every day but we practice when he does. He's very exciting.