Putting a cage on a puppy's face/mouth is not the answer. Puppies bite, nip and play. It's how they explore and learn. Repetition, teaching, correcting and redirecting is going to be the answer, in short work. They can learn and you just have to find the right method for your pup. Its frustrating, yes, but be patient as they mature they begin to understand what hurts and what does not and will become more gentle as you teach them. At 8 weeks she is teething, exploring and playing like a baby which is exactly what she is! She will be teething for quite a while, once her baby teeth are all in, the process begins again with loosing them and regaining adult teeth. Teething does account for alot of the mouthing. Cruiser was a major pain with biting, nipping and over mouthing. At five months he is now doing quite well and has learned that it is ok to mouth without pressure. He has become very aware of his teeth and watches you when he does grab your hand or arm in play. It took alot of work and patience and was a very difficult process, but we worked through it with success! Keep trying different methods or combine techniques, they will work!