Notched leaves on your rhododendrons are caused by a variety of species of weevils. The adult forms of the weevil tend to feed at night during the springtime when you're resting after a hard day in the garden. The damage will not kill your plant, just cause unsightly notching on the leaves. Of course, the leaves being evergreen will be around awhile to annoy you.
One method of control is to go out to your garden in the evening with your flashlight and pluck the weevils from underneath the rhodi leaves and toss them into a bucket of water. This never appealed to me.
Another, more toxic method is to spray with a systemic insecticide, like Orthene. Make sure to follow the instructions on the label. Soak the leaves, both top and bottom as well as the soil underneath to get the best control.
The third method is to allow for a measure of acceptance of the notches and let nature take its course. Your neighbors will either respect your concern for the environment or talk about your lack of concern for aesthetics.