Defiant 18 month old......

My son will be 18 months on the 22nd, and is sooooo defiant. When you tell him “no” he thinks it’s funny and does the Naughty activity ten fold. He doesn’t listen, pays no mind to trying to correct behavior, and will repeat over and over. I’m really struggling over this. I don’t want to have the kid in the room that doesn’t listen.