Did your dog tire out when you ran a marathon together?

Yes

You should never TRAIN your dog like an athlete! You should not think of him as trying to get stronger, take it on small workouts not a marathon. It could get hurt from all that running at once.

Dogs are short naturally distance runners, humans are natually long distance runners. It gave us the advantage even before ancient times because we could easily outrun predators and catch food. If you train with your dog often you might be able to work around this.

no, but if yours did, i would say next time that you should have him workout with you, just so he is conditioned, just because he is a dog dosn't mean he cant get tired (although it may seem like that)