Unfortunately sometimes dog diarrhea is hard to pinpoint but it could be stress or even some underlying infection. Does your dog tend to eat things you aren't aware of? I know when my pup was young, almost everything went into her mouth (many times without me seeing).
Your dog could also just have a sensitive stomach. If i stray from my dog's diet even a little bit, she gets the runs.
If your dog is healthy enough you could try fasting to see if there is something in his system that needs to be flushed out. I also have used marshmallow root in the past that has helped my dog. For a full list of other causes and remedies, I recommend reading Dog Naturally's Dog Diarrhea article.
Your dog could also just have a sensitive stomach. If i stray from my dog's diet even a little bit, she gets the runs.
If your dog is healthy enough you could try fasting to see if there is something in his system that needs to be flushed out. I also have used marshmallow root in the past that has helped my dog. For a full list of other causes and remedies, I recommend reading Dog Naturally's Dog Diarrhea article.