Is it your dog? I suggest you seek advice from a professional trainer. There's lots of advice online - but if the situation is dangerous, you should get help.
If it's your neighbor's dog, try speaking to them about your safety concerns. If they don't take you seriously, you may need to register a complaint with animal control.
Most dogs that are labeled as aggressive are actually afraid an reacting to that fear. Both my dogs are like that. One has been ganged up on in a dog park, twice. I have worked with her and can take her for walks as long as we keep an good distance from other dogs. We were doing really well when someone else's dog snapped at her and set us back at least 6 months in training. I now do not allow any dog I do not know within 25 feet of her.
My other dog is a rescue so I don't know what started his fear. If I am walking him alone he does well, but with my other dog they seem to feed of each others fear.
If it is your dog, you need to find the trigger and retrain for that trigger. A good trainer can help. Often times it is something the owner is doing that triggers a dog, so it is good to get the perspective of a trained eye.
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