Answer: The answer is going to be to some extent a matter of opinion, budget and so on. You could use the same again, or possibly use the preformed concrete units formed specifically for this purpose, or go with natural stone or even poured concrete. You may want to check some of the many books available on building retaining walls to begin evaluating the options. I would strongly suggest you work with a professionally trained landscape architect or landscaper with extensive experience in building retaining walls to design one that will be both long lasting and safe, then proceed depending on your skill and comfort level with either hiring it done or doing it yourself.
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