Try giving treats as you are trimming his nails? My GSD x BMd use to do the same thing I ended up having to muzzle him to trim his nails as he use to hold onto my hands so hard that I would have indents from his teeth. My dog now a BC just lays there and lifts each leg up for you to trim what a difference, he is so easy to do.
A man who looks into a collie's eye to receive an icy stare is but a fool. Be at one with man's best friend and through his eyes you will see his very soul.