Installing a retaining wall yourself will give you a headache and also hurt your wallet. Because of this, there are professional contractors who will build retaining walls for you. Retaining walls tend to be AT LEAST three feet high, and are well over three feet long. The higher and longer the wall is, the more work will need to be put into it. If you are new to retaining walls and finding contractors for the job, be sure that you find several names on the Internet, the phone book or from family and friends and then interview them.