If I have a List in a Grails domain class, is there a way to override the addX() and removeX() accessors to it?

In the following example, I'd expect MyObject.addThing(String) to be called twice. In fact, the output is:

Adding thing: thing 2

class MyObject {
    static hasMany = [things: String]
    List things = []

    void addThing(String newThing) {
        println "Adding thing: ${newThing}"
        things << newThing
    }
}

class BootStrap {
    def init = { servletContext ->
            MyObject o = new MyObject().save()
            o.things << 'thing 1'
            o.addThing('thing 2')
        }
        def destroy = {
    }
}