If your dog needs sedation to be groomed, you should make an appointment with your veterinarian to examine the underlying cause - is the grooming facility or handling by the grooming staff causing anxiety? Does your dog have separation anxiety? Does your dog have an underlying metabolic disturbance that is exacerbated by the stress of grooming? If the problem appears to be a learned behavioral problem (associated fear/anxiety/aggression), a veterinary behaviorist or certified dog trainer may be able to help. Be warned - retraining a dog to overcome the learned fear/aggression is a very long process and may take a year or longer. You will need to work with a veterinarian for grooming needs during this process - your veterinarian is not a groomer but he/she should be willing to trim down a dog's nails or hair coat under sedation when it is a temporary resolution.
Your dog should not be under chemical sedation without a veterinarian being on site at the grooming facility - a veterinarian needs to be available in case there is an unusual reaction or the sedation needs to be reversed.