How Do I Make My Dog Stronger?

Just like you would yourself:  Plenty of exercise, rest, and especially: Good quality food.  Your dog is a canine, a meat eater, and his or her kibble or wet food should list some kind of meat as the FIRST ingredient, showing that is the main ingredient.  Take your dog out for walks, and to dog parks where he can be let off the leash to run and play Frisbee or fetch with you, or just to run with you.  Make sure you bring water for your dog just like you would yourself; you can pour it into his mouth.  The stronger your dog becomes, the better shape he gets into, and I'll bet the same thing happens to you.  Many Blessings,
Ladywitch

Make sure that he has plenty of exercise and give him the right amount of dog food to eat

Feed him a good lean protein diet(not that purina crap where the first ingredient is corn) and make him run a lot