I have a customer that would like to replace a rotten wood retaining wall. They would like 2 man rock. The wall is 4' high x 50' long. As I have built a few before I have some questions. 1.) How should I incorporate some drainage through the wall? I have seen some walls that had 2" drain pipe built into the wall to allow water to drain through it. It rains here (Seattle) and I am sure it would be best to do this. There is a drainrock filled trench in front of this wall for this water to go into and drain away. 2.) I will be backfilling with rip rap, should I also put in a barrier between this and the dirt behind the rip rap? Thanks for any information....................again!