I take my border terrier on hikes and we both love it. The only problem is that he's a snuggler so I tend to get pushed off my sleep pad at night.
The most important things to consider have to do with the health and safety of your dog.
1. No offence to Mr. Dent, but even when my dog was a puppy he could handle more than a block on concrete. In fact, he never had a problem with concrete and would never needed to condition himself for that. However, trails, gravel, etc are a different matter. So, you need to be taking your dogs on short dayhikes, longer dayhikes, then an overnight, then a few nights, etc. See how the dog does at each level. If he handles it no problem, and i mean no problem, move to the next level.
2. The other issue is obedience. You need to train the dog to sit, stay, etc. basic stuff. You also need to teach him to stop. I would take my dog's favorite toy (tennis ball), go to a field, and play fetch for a bit. I would then throw the ball, let him run a few yards, and then command him to STOP. Now the first few times he didn't - but he doesn't get rewarded for that either. After some repetitions of this, the dog will probably stop to see why you're giving him a command when he has to get his ball. Reward him then. Keep going and he'll get it. Try to keep training sessions short - 15 minutes or so. Also remember to socialize your dog as much as possible. This will curb the tendancy to bark at everything.
Of course, the only sure-fire way to ensure your dog stays with you on the trail is to have him leashed. And just as important as it is for you to have the right gear, don't forget the dog's needs. Something soft/warm to sleep on, adequate food and water - something to chew on if he's bored.
I think it's awesome that you're looking at a rescue dog. You'll be able to gauge the dog's temperment when you go to the shelters. Good luck!