First I want to respond to the spanking replies, then I'll give you some other ideas. If your child is nine and kicks and bites you when you try to set limits, then spanking is not the correct course of action here. It could end up in a brawl! That would obviously not be helpful to anyone and could end up crossing the line to abuse.

Most experts do not support spanking including the American Academy of Pediatrics. According to (the few) experts that do support spanking, spanking after age 10 is inadvisable. Den Trumbull MD says: "Spanking is inappropriate before 15 months of age and is usually not necessary until after 18 months.  It should be less necessary after 6 years, and rarely, if ever used after 10 years of age."  

As a parent coach and educator, I don’t tell parents whether or not to spank- that is a decision each family must make on their own and with great thought and correct information about the pros and cons.  My job is to provide parents with information to make a good decision for their family. In fact, I’ve written an article about the different points of view on this so that parents can be informed.

If you or anyone else here does decide to spank, doing it correctly is very important: No anger, only as a last resort after other methods have failed, should be a planned action (not a reaction), child should be forewarned about “spankable offenses,” done in private,  one or two “spanks” on the buttocks only, lots of love and hugs afterwards, and a sense of remorse should be present in the child.

If there is no remorse and resulting closeness with the child, or it only escalates things (like it did with my son when he was two which was why we stopped spanking and thankfully discovered Love and Logic) then spanking is not an effective disciplinary response for this particular child.  

For me and my family, we made the decision not to spank. A key component of a good parent/ child bond over the long haul is treating children with respect and dignity and I haven’t figured out how to spank respectfully. :-)  Plus, I worried that spanking my children could come back to haunt me in the teen years…

That being said, the poster is correct that your child needs "something" to teach him about firm limits and respect for parental authority. I am going to copy my reply from a similar post on this forum because the answer is also relevant to you. This other mom's child has ADHD and ODD (Oppositional Defiant Disorder). Her question was “How do I deal with a problem child?” Her son is eleven:  

This question can't be answered in a Q&A forum, it is really a counseling or coaching issue.  
 
I don't want to sound like a commercial, but the best advice I can give you is to take the "Becoming a Love and Logic Parent" class which is probably offered somewhere in your community (do a google). This class will give you the answers you seek- or at least the foundation to begin making healthy changes in your home. Love and Logic also has books, but this class is what will help you because of the video clips and the interaction with other parents and the facilitator.  Many counselors recommend L&L along with therapy.
 
One thing I can tell you is that with resistant kids, it is especially important that you use choices instead of demands and learn how to set limits without saying the word "No." That little word just gives them a reason to fight. So try this instead:
 
Say Yes Instead of No!
Parents can still set limits and say 'Yes!' by using the following phrases:
• "Yes! Just as soon as ..."
• "Absolutely! Right after..."
• "Yes! And..."
• "Sure! As long as ..."
• "Great idea! But first..."
• "Yes, if..."
 
Be sure to put the emphasis on the word "Yes!" with great enthusiasm and big smiles. It helps to pause for just a moment right after the 'Yes!'  And then say, "as soon as" or "right after", etc.
 
Examples: "Can I watch TV?" "Yes! As long as your homework is done."
 
"Mom can I have that?" "Absolutely! Just as soon as you earn enough money to pay for it!"
 
Here's one for teens: "Hey Mom, can I borrow the car to go over to Bill's house?" "Sure! Right after you're done mowing the lawn."
 
Remember, the key is to be cheerful and encouraging as you deliver your message.
 
It sounds simple but is amazing how well it works.
 
Another thing to remember is that anger and frustration fuel misbehavior. So if you are responding to your child with anger and frustration (and who wouldn't?! You're in a tough spot), you could be making things worse. Love and Logic will give you some tools to replace anger responses with. Check out their website- there are many free articles and a good free audio which will help (www.LoveandLogic.com).
 
There is also a good free audio by the co-founder of L&L on the website I manage at: www.ParentingChildrenWithHealthIssues.com. The audio will really help you as it directly addresses the frustration/ sympathy issues parents often face in situations where a kid has health issues and is resistant.
 
Good luck and hang in there. There is hope! I've seen 1000's of lives change with this material (including my own).
 
Lisa G.
Parent Coach and Mom
Co-author of "Parenting Children with Health Issues"

Sounds to me like regression.  Sometimes kids, especially kids with ADD, ADHD, and kids who are Autistic, revert to younger age emotions as a way of dealing with stress.  Check into what is going on at school (ie, bullying, fights with friends, being picked on, etc.), and also look to his home life.  If there has been a serious problem in his life, like the death of a family member that he was close to, separation of parents (divorce) or even the birth of a new baby, it can be traumatic enough to bring out this regression in demeanor.  If there is no cause of this "attitude" you may want to ask your son's psychiatrist about ODD (Oppositional Defiance Disorder).  My son was diagnosed with this on top of his ADHD.  There are no medications to deal with this disorder.  It needs to be dealt with, by working closely with his psychologist, and looking up as much information as possible.   Here is a good place to start, if ODD is in fat an issue for your son.