This is an objection often raised by atheists. Many think that Christianity teaches that God arbitrarily assigns rules for moral behavior, and that his ability to enforce those rules is the basis of right and wrong. But this is not the Christian position. God certainly has the ability to enforce the rules he reveals to us, but what is morally right with God is due to his character--not his power. The reason it is wrong to lie is that God cannot lie (Titus 1:2). Therefore, right and wrong are not determined by God's ability to be stronger than anyone else. Right and wrong are determined by God revealing his own immutable, holy essence.
Whenever an atheist accuses Christian theology, and in particular the Christian God, of determining morality from "might makes right," he is misrepresenting the Christian faith. But, this is often the case with atheists who fail to seriously study what they criticize.