I bought a pedi paws which is a low power battery operated Dremel style tool. I have heard that with bigger dogs there is not enough power in these tools, but I am in no hurry and would rather work a little harder than to quick a dog. Poop usually falls asleep upside down in my arms while I am doing his nails.
I use a manual cutter, backwards, so the blade cuts front-to-back, opposite the way the blade guard is designed for. Front-to-back seems more with-the-grain. Have an assistant distract the dog if it's scared. Al used to scream bloody murder; now I can do him without help. Cut after bathtime or a walk int he snow/rain; claws are much softer when they're wet. Mark it on the calendar so you can figure how often to do it. Cut often, cut little. I put them upside-down between my legs on the floor. If you don't hurt them, they'll get used to it.