K.,
I have a 20 month old son as well. He started the testing about 3 months ago. Here is what I have learned with the little guy:
#1 Consistency
Select 1 behavioral correction method and stick to it. I found one called the SpRD (stop pause redirect). You and everyone that cares for your child must be informed of this method and use it. Including Dad!
http://www.amazon.com/Manipulative-Child-Resilient-Resour...
You can pick the book up at the library and go straight to the chapter that discusses how to use this method.
#2 Creativity
My little guy is very much like his dad and that is he has inherited his High IQ. In order for me to stay one step ahead of him, I must use creative thinking.
For example, he started the not wanting to leave the car seat when we arrived home. He absolutely loves to go places and meet new people. Anyway, instead of forcing this child to do as I say. I remembered the old saying, "You can lead a horse to water, but you can't make him drink." My son is wise for his age. So, I invented a game called "Hunt the Monkey." I tell him there is a monkey loose in the house and we must find it (stuffed curious george). This drove him crazy the first time we did it. The excitement in his eyes was unexplainable. Anyway, creativity outsmarts stubbornness any day.
#3 Be Mommy Cool Cat
They must never see you loose your cool...no yelling to get them to do what you want. Always, always use logic, reason, understanding, empathy, and most important love when disciplining the little guy. If he loses respect for you, you lose him. Lots of deep breaths.
#4 Mr. Strong Arm
One Mom below is correct...I have noticed this with my husband. Boys listen more to their dads than their mothers. HOWEVER! We stay consistent on all our disciplining. The only time he jumps in is if our little guy is going into combat mode. Then, Daddy steps in and stops the bad behavior. Let's face it, we all have our bad days. He is a little guy and needs a strong voice every once in a while. Kinda like when we are going through a difficult time in our lives and only a fellow woman can help mend us back together.
Creative suggestion for throwing food....Grab his favorite toy...place it by his high chair during one of the next throwing episodes....pretend to be the toy speaking...say, "name of child, I do not like what you are doing right now, I am going to go away for a few days and come back when you are no longer acting this way. I like to throw things outside, but do not like throwing things inside. Bye-Bye for now." Then, walk the toy out of the room and come back. Children at this age are highly receptive to being sympathetic to hurting others feelings.
Good luck! Oh yea, I speak to my little man like he is 4 years old. He understands the English language very well. Maybe your guy is the same way. Just tonight I started making him go to sleep in his own room (co-sleeper/nurser). I had to tell him that Mommy was going to be in the next room and as soon as he fell asleep, I would pick him up and take him to bed with me. This was the only reasoning method that stopped the stomping and refusing to sleep mode. He immediately climbed in his bed and went to sleep on his own!!!! Telling him he is a big boy now, blah, blah, blah, did not work. I had to become empathic to his feelings and think about what would make him go to sleep on his own.
My husband and I are learning every day, as this is our first child. It is definitely one of our best adventures together. Good luck to you and your husband.