Hi, I'd like to help you with your question.
I am so sorry to hear about your dog. It is always hard to deal with the loss of a family pet since they are so much a part of your life.
Approach your son about Chicca's death very directly. Be sure you are in a private area so that he feels safe and able to express his emotions then tell him what happened. He is 9, so developmentally he does not need any special explanations. Express your sorrow about the loss. Allow him time to process the news then let him know that whatever he feels about the loss is ok. Offer to let him talk to you or his mother anytime he needs to. Then stay available as much as you can. Answer any questions he has honestly. It is tempting to try to take the edge off the truth so he is not hurt by what he hears. But kids at his age can tell if someone is not being truthful so being honest will help him trust you.
Unless he has experienced a death before, it is hard to predict how he will react. Some kids become upset and cry a lot, others withdrawal, and some become angry. Many kids want to know why and some don't want to talk about it. But no matter how he reacts, as long as he is not acting out and hurting himself or others, he should be allow to express how he feels.
When you feel he is ready, ask him to help memorialize Chicca. It is part of the healing process to say goodbye to a loved one, and this also helps people feel like they can do something for their pet. You can do anything from having him draw a picture to naming something after his dog or putting together an memorial picture book. If you bury your dog, he can help make the marker or help choose the marker. Anything that he feels will help him express how he feels about Chicca.
Whatever happens, don't talk about getting another pet until you and your son feel that everyone has had adequate time to mourn Chicca. Getting a pet too soon could cause your son to feel guilty for leaving Chicca behind and as a result, he may take it out on the new pet.
Here are some resources to help your son:
The Forever Dog by Bill Cochran and Dan Andreasen
Goodbye, Friend: Healing Wisdom for Anyone Who Has Ever Lost a Pet by Gary Kowalski
You can find these books on Amazon.com or your local library may have them for you.
The most important thing to remember is to keep the lines of communication open and allow your son to express how he feels. If you do that, he should be just fine.
I hope this helps,