A normal collar is fine for taking your dog on a short walk, but for serious hiking, he'll be safer and more comfortable in a full body harness. Before you run out and buy one, try to make your own with paracord.
Instructables user mymyjames2000 shows you how easy it can be. You'll just need some paracord, plastic buckles, and a candle. He shows you how to properly tie the paracord into a harness, attach the buckles securely, and fuse the loose ends of the cord with a candle to prevent them from fraying.
It doesn't look too difficult, but it does require lots of fairly complicated knot tying, so be sure to set aside some time before taking this on. Once you're finished, the harness will fit snugly around your pet's midsection and neck to distribute the tension of your leash more evenly.
Paracord Pet Harness [Instructables]