Actually, he cannot understand your explanation at this age, as you are probably realizing. Not only that, but he has a good intent and a real need behind his actions.
It helps to understand WHY he is driven to do this. Only then you can help. Most often he is just needing a sense of power and play. I played with my children in situations like this and it vanished fast.

Read from page 200 on (or the whole chapter starting page 193) of the book, Raising Our Children, Raising Ourselves. It will show you how to help your child and how to turn the whole thing into therapy and joy.