If I do see a dog or puppy eating dirt, they get dosed with a half-teaspoon of bentonite clay each day for a week. I have found that this stops the dirt eating almost immediately.
For a point of reference, our dogs weigh 55-75 pounds. For a smaller dog I would use much less and a larger dog might need more. Occasional use of small doses of nutritional clay has no reported side effects so you can play around with dosing until you feel comfortable with the results.
Again, this is not a “more is better” situation. Occasional small doses of nutritional clay can have great probiotic properties and provide important trace nutrients. But large doses of clay over time can bind up other necessary nutrients and cause health disorders. So, moderation is key.
Do your dogs eat dirt? If you try adding nutritional clay to their diet, let us know how it worked for you - did it stop the dirt eating?