Dogs can tolerate aspirin well, but I'd give him the low-dose aspirin or children's aspirin, 82mg vs 325mg of the full-strength. Also, get aspirin that is enteric coated, this will make it easier on the dog's stomach. There is a special aspirin called Ascriptin that is coated with Maalox. I don't know if it comes in the low-dose variety or not, but this would be ideal if it does. If not, just look for low-dose, enteric coated aspirin.