Nature's Remedy is a good homeopathic to deal with stress, but it isn't likely enough to overcome the state of terror he is experiencing. I'd recommend a long slow program to try and desensitize him to the nail clippers. And in the meantime, there are medications to safely tranquilize your dog, but talk to your vet about them - each breeds can have different reactions to some drugs, and generally speaking except most drugs made for people are bad for dogs, and aren't dosed right.