How do you solve a problem like Seth?

He'd outpester any pest
Drive a hornet from its nest
He could throw a whirling dervish out of whirl
He is gentle! He is wild! He's a riddle! He's a child!
He's a headache! He's an angel! He's a boy!
How do you solve a problem like Seth?
How do you catch a cloud and pin it down?
How do you find a word that means Seth?
A flibbertijibbet! A will-o'-the wisp! A clown!

"The Sound of Music" fans might recognize these words, I merely substituted "he" for "she" and changed "Maria" for "Seth" but it describes very well how I feel about my boy today.
He will not listen, he talks back. He runs away in public places, he hits his brother. This kid is very intelligent but super stubborn. And David and I are at a loss as to what to do. We yell, we swat his bottom, we send him to his room. We withhold things he likes and tell him we will reward him if he's good. Nothing seems to work. David had to really spank him tonight and he didn't laugh this time. I hate to be a mean parent-maybe that's why he's gotten this bad. I hope he grows out of it. Bleh.