Protect ArrayList from write access

Consider the following class:

public class Cars extends Observable{

    private ArrayList<String> carList = new ArrayList<String>();

    public void addToCarList(String car){
        // ...
        hasChanged();
        notifyObservers();
    }

    public void removeFromCarList(String car){
        // ...
        hasChanged();
        notifyObservers();
    }

    public ArrayList<String> getCarList() {
        return carList;
    }    
}

As you can see, every time the carList is changed, I want to notify the Observers. If someone does getCarList().add(...);, this is circumvented.

How can I give read access to the carList (for iterating over it etc.) but prevent write access to it except for the special methods addToCarList and removeFromCarList?

I thought about this:

public ArrayList<String> getCarList() {
    return (ArrayList<String>)carList.clone();
}

but someone using my class would, when adding something to the clone of carList, not be informed that that's not the way it's meant to be done.