My fiance and I got a puppy last year, which happened to be our first season backpacking as well. He was fantastic, but mainly because he was so tired at the end of the days that he didn't have enough energy to care about chasing anything, or ruining anything (he once fell asleep while a porcupine walked about 1.5 feet away from him...never noticed. Course, neither did we till it was much past us).
Now that he is MUCH bigger and has alot more endurance, I'm a bit more concerned this year. I have been training him to bike with me, and find that the stop, go, and on by commands will certainly help while backpacking. I'd prefer to be able to keep him off leash as it's less annoying for everyone involved, dog included, but won't risk it until he is fully trained with his new commands.