I am unfamiliar with nut pinching, however, the force action I am familiar with is applied via pinch through the ear. The only thing in your post I am arguing is the word "severe". From what I have seen, professionally, it is quite humane. Not to mention the expediting of the actual fetch. I also have had a vascectomy, so yes, I can have a take on the goings on down there. It sounds like you have a great dog, coupled with a trainer who has his own ideas of proper training methods, and thats great too. I wish you both the best of luck afield.