Idea Exchange: Use a towel to calm fractious dogs
When drawing blood from or trimming the nails of difficult large dogs (especially ones that continue growling and being aggressive despite being muzzled), place a small folded towel over their eyes. Your assistant may need to hold the towel in place. Covering their eyes should calm these dogs down; however, they should remain muzzled. This out-of-sight, out-of-mind technique has worked well on 120-lb German shepherds and rottweilers, as well as smaller dogs, cats, and rabbits. Some owners even end up using this technique at home.
Dr. Christine Sherden