"Can God create a rock so big that He can't move it? Wether you answer yes or no, it means there's something God can't do. Therefore, He can't be omnipotent."

The objection is flawed because it hinges on a fake definition of omnipotence that requires the ability to do all things, including make oneself fail. This built in contradiction is designed to make omnipotence impossible by definition. And since there are many things God can’t do such as lie, tempt someone, or deny himself, then He obviously isn't omnipotent according to this definition. However, if we stick with the actual definition of the word (unlimited power), then the objection falls apart. 

The answer is that God can’t make a rock too big for himself to move because He’s omnipotent. There’s no limit to the size of rock He can create, and there’s no limit to his ability to move it. God’s “inability” to make himself fail (make a rock he can’t move) is a strength, not a weakness. To say otherwise is merely a word game and does nothing to discredit the God do the Bible.