I use mainly time outs with my daughter. I believe its OK to spank as long as you are not doing it from anger and frusteration and only for disapline.

Something you might want to try though time consuming. Take everything out of your sons room and store it where he can not get it. Every toy, extra, fun thing. Leave only the necessary items like the bed, blankets, ect. As time goes by with good behavior he can earn back his stuff as well as lose it again with misbehavior.

What ever disaplin you choose stick to the set consequences you set. If you give in even once you teach him if I push long and hard enough I will get my way. So If he is in time out for four minets even if it takes four hours to accomplish it stick to it. It does get easier over time.

also look for outside help like parent aid program, or help me grow.