I have seen so many dogs with problems and feel through my experience having dogs and horses has helped me realise the benefits of Clicker Training and positive reinforcement.
This can be started as soon as you have brought a puppy or you have a dog that you have just got or a dog that you have had for a while and has some problems you want sorted.
You will find this approach a lot of fun for you and your dog and your dog actually thinks they are training you to get a reward so its a wing win.