To increase the effectiveness of any deer deterrent you should use two deterrents that offend two different senses. For example, both Irish Spring soap and coco bean shell offend the sense of smell. If you used hot pepper wax, which offends the sense of taste, in combination with either of these you would have better luck. See the following page on the My Deer Garden web site for more information. If you have some wooded property near you that is probably where they sleep.
Deer eat different things in the winter than they do in the summer.
That is because their bodies can not digest the same types of food in the winter as in the summer. In the winter time they need to eat very fibrous things, such as twigs. They can not digest leaves and grass in the winter. Their stomachs can be full of leaves and grass in the winter and they will still starve. For this reason the deer probably will not bother your holly and Rhododendrons much in the spring and summer.