I have used the peroxide on an American Bulldog that ate my sweatband. I gave her a tablespoon. She regurgitated it up. I had to quickly get it because she was going to try to eat it again.
Garlic was also used at one time as a natural flea deterent. It was common to get brewers yeast and garlic supplements. But it has since been determined that garlic is poisonous to dogs. However , it will take a large quantity to harm a dog. I have stopped using garlic.