If you have a dog that is very hard headed and difficult to train, you need to do your research on shock collars to choose the best one for you. There are many different manufacturers which lead to many different choices for you. There is a wide range of stimulation can be used for correction.  This stimulation can range from a little tingle to a short term of extreme discomfort for your dog. It should be up to you, and to what extent your dog needs correction. Just remember the lowest stimulation level that is needed for your dog is the best for him.