Your dog can get into a lot of trouble while out on the trail, and it's your job to do everything you can to keep it safe. This means paying close attention to the dog's needs. If it's panting, then break out the water, because dogs can't sweat like we do when they get hot. You can buy collapsible bowls and other gadgets if your dog won't drink from a water bottle. And don't let it drink from a stream or puddle; these can be full of nasty bacteria like Giardia. Not hiking during the hottest parts of the day will also help to avoid dehydration.
If your dog isn't wearing booties to protect its feet against rough terrain or the weather, stop periodically and check its paws for cuts. And if you're hiking in an area where you might encounter hunters, get your dog a bright orange vest or bandanna so it isn't confused with something else.
You also need to worry about other dangerous threats, like snakes. Dogs will notice wildlife sooner than you do -- another reason to keep them on a leash. Make sure they know "leave it" or a similar voice command. In the event that your dog is bitten by a snake, try to keep it calm and use your first aid supplies. Call your vet as soon as possible.
Poison oak or poison ivy can also be a real menace while hiking. If your dog does get into a patch despite your best efforts, you'll need to bathe it as soon as possible while wearing gloves. It's more likely to affect your skin than your dog's. While they're most likely to just roll in it, some dogs will even eat poison ivy leaves and may need to take activated charcoal and IV fluids at the vet's office.
At the end of your hike, check over your dog thoroughly. It may have picked up a tick. If you do find one, use your tweezers to grab the tick as close to the skin as possible and pull it out straight. Keep the tick if possible so it can be identified if your dog gets ill. If you can't get the tick off, a trip to the vet is in order. Also, check for any scratches or abrasions on your dog's skin and treat them accordingly.
With any luck, now you've found another fun activity that you can do with your dog, and now you know how to keep it safe and happy while hiking. Happy trails!