I have a chow/shephard mix(female) that was 10 yrs old when rescued from a not so hot situation. She had been crated her entire life(with walks) at a vets office for use as a sort of live in blood donor dog. At 10 years the vet decided she was too old and threatened to put her down unless a rescue organization took her. They did, and i was the lucky person who adopted her. She is an amzing girl, sweet and loving, but she hates having her feet and nails dealt with. What i started doing:

every night i would simply stroke her fore legs, as far down onto her foot as she would let me. Every few days or so i would go a little further till she pulled away her foot. Then of course when she began to let me stroke her paw, i would begin to massage(very lightly) her toes, especially where they seperate from each other. Then i began to bring my face closer to her foot to inspect the toes and when she wasno longer fearful of that(both the touch and closeness combined) i began to seperate the toes to feel inside them. She now tolerates that pretty well most of the time. AT NO TIME does she gets forced.She will sometimes let me keep hold of her foot and i have been able to clip ONE nail, and i am hopeful that over the course of the next 6 months she will allow full handling of her feet.
Hope this helps you out, and that you can calm your dog down. Is the dog otherwise fully trained?