It seemed that every year I taught confirmation class to 7th and 8th graders I would get some variation of the question, "Can God make a rock so big He can't lift it?"
The answer is "yes" but I never felt like I gave a really good answer to the question. Then I discovered this from letusreason.org:
Can God make a rock so big He can't lift it? If He can't lift it He is not all powerful. Then the rock has more power than God and whatever is more powerful than God is God.
If God can make it, He can lift it. If He can create it, He can destroy it. What He creates is under His jurisdiction, under His control. It can never have equality.