First of all one should consider using rocks or boulders with character in medium up to large sizes in almost any landscape theme. I personally use them even in formal designs and believe they add interest.
Secondly I have known designers that have based their entire plan on the tasteful use of rocks. However, one should always incorporate plants into an otherwise all hardscape design to help to soften the overall impression.
When using an abundance of stone on a project one should give consideration to adding a water or bog garden or both along with a babbling brook. Water and stone along with proper plant selection always go gracefully together.
In developing your own ideas for what you would like to see in your yard, sit down and thumb through an assortment of magazines and books on these three major areas of landscaping which are:
Plants
Water themes
Hardscaping
Consider hiring the best designer that you can locate to develop along with your input a truly knockout landscape concept.
Your home landscaping should be for your viewing pleasure and welcome you into your driveway each evening as you return home.
The back yard can be an oasis to help you relax from the various stresses experienced throughout the day.