I think the best thing to remember is that the health of a dog, or a human, is largely a reflection of what the diet is made up of. So, if you're dog is eating highly processed foods that smell rancid because the oils in them turned long ago sitting in a warehouse waiting to be shipped, there's a lot you can do beyond that. That's not a diminutive comment, it's food. Although, it might explain why you're dog smells like low quality oil.
Beyond that, here's a remedy I've found for diarrhea.
Diarrhea or Loose Stools: There could be a number of causes for this in dogs. It's important to remember that just because you can remedy the symptoms doesn't mean that the underlying cause of the problem is cured. If you're dog has worms, you can help with the liquid shit that comes out, but you're just going to extend the issue if you don't treat the worms. They have a short digestive tract, which usually deters certain bacteria that could easily squat in our guts from setting up camp in theirs. That said, shit happens.
One of the most effective, and cheapest remedies I have used for this is a teaspoon of cinnamon cooked into one cup of rice. There's a myth that dogs never ate grains in the wild. It certainly may be true that they didn't eat sticky rice, but they did eat animals that ate grains, and they're carrion eaters, they ate the grains and vegetable when they ate the guts. Either way, this is a simple thing to prepare, easy to find and afford. If you can't make rice, buy some, and stir the cinnamon in, although I'd use less, like 3/4 of a teaspoon if you're not cooking it. You should notice results in less than a day.
Keep an eye on the excrement, and keep this in the diet for at least two days. I've used blackberry leaves as well, as a tea to cook the rice, but it's more astringent than cinnamon and I wouldn't use unless the cinnamon doesn't work. If you're dog isn't interested, try throwing some meat into the water as the rice cooks, or putting some oil and a small pinch of salt into it. Oatmeal works well instead of rice.