Examples of giant breeds are Great Danes and Mastiffs. All dogs need regular medical care. Having a working relationship with your vet wil help ensure you have a healthy pet. Different dogs were bred for different reasons. Please be aware of what the dog you want was bred to do.
Training is a key element.
Most dogs are turned into Humane Societies and rescues because they aren't trained. Habits like barking, digging, chewing and pottying can all be helped by training. There are many fine training programs available, through private trainers and community education classes. Another important consideration is what breed of dog you are looking at adopting. There are many different breeds of dogs and they were all bred for specific purposes.