Different people behave differently and have different needs and different minds. The same goes for dogs. Some dogs are calm and friendly by nature and will not show any aggression whatsoever while others can easily display their aggression, even when only slightly provoked.
What can you do if you get an aggressive dog or a dog that bites? There are a few options, but before you start seeking help from professionals, ask yourself: "Why does my dog bite or is overly aggressive?" If you already know the answer, then you can try training your dog to avoid this unwanted behavior. If your dog bites when someone tries to touch his toys or food, then either tell everyone in your household that they should not touch his toys or food (passive solution) or stand in front of him and firmly set your rules and show him that you are the leader and not him (active solution). If he shows aggression, take his food away for a while or his toys until he calms down. Show him that you mean business and that you will not let him treat you that way. You have to be patient and consistent at whatever you try to teach your dog.
If you have tried removing your dog's aggression yourself and it has not worked, seek professional help from a dog behaviorist or dog trainer. It is better than giving up on him and dumping him at a shelter where most likely he will get euthanized or put down because of his previous history of aggressive behavior and biting. The professional behaviorist may recommend to you to rehome the dog with someone who has more time to work with the dog and has more experience with your dog's breed. If you have small children, and the dog keeps biting them, the best solution would be to rehome the dog as small children do not understand things like adults do and may not be able to always follow our instructions regarding how to behave around the dog. I think that you will agree that rehoming is a much better solution for both you and the dog than euthanizing the dog that may still be able to live a happy life with someone else.
Even the dog that had been labeled as vicious and aggressive can find a good home with someone who understands what the dog's needs are and how to avoid being attacked by this dog. Some dogs may show aggression because they are bored and frustrated and need more exercise and mental stimulation. Some dogs may bite people because they have been traumatized in the past and are afraid of people. Some dogs may be ill or feel pain and, as a result, they will not be in the mood to be touched and may bite people who come too close to them. This is why an aggressive dog should be checked by a veterinarian before even hiring a professional dog behaviorist or trainer because if your dog is sick, they will not be able to help your dog.
Whatever you do, consider you options and do not give up on a dog too quickly. Be patient and do whatever is in your power to help your dog overcome aggression and biting. If you are not successful after trying all of your options, consider rehoming your dog. Leaving the dog at the shelter to be euthanized is the last thing you should consider when all else has failed.