I know from experience that life with a child with defiance can be very trying. Especially when they are so young and have so much to say, but cannot. In my family, the use of sign language in combination with speech/language therapy proved to be most helpful. It allowed our son, who had some speech and language difficulties, the ability to express himself calmly and accurately, thus reducing frustration and behavioral outbursts. We used it as a bridge until the speech and language abilities could catch up with his cognitive skills. We also let him use art and play as a way to communicate, too.
Also, you may find some help with these great websites, books and articles, as well.
I have been a daycare provider ( and mom!) for 17 years. It seems to me that the children I have with speech delays typically act out with more aggression. I truly think it is there lack of speech that makes this more presentable in these children. They can't communicate the way they need to and find that being aggressive or defiant typically gets them what they want. I use a great in home speech website called Speechtails with several of my kiddos and have found it a great tool. It gives me tons of tips to help encourage speech and a great program. Give it shot! hopefully this stressful time will pass!!! Good Luck, Vikki B, Indiana