it's gradually degrading, everything is gradually settingdown and flattening out. how quickly does that happen. as we look at retaining walls you see things a short term solution, how long are you trying to preserve this? how long would it last? >> probably 30, 40 years. one thing to be careful about, wood retaining walls after being made out of pressure treated wood or dry rot resistant wood which is generally clear hard and redwood. all pressure treated wood were copper arsenic suetion solution. when it got wept it would leak out the larsening and kids would put the hand on the wood and put their hand in the mouth, and they were getting lars anything. >> they changed the formulation of the pressure treated formula to prevent the hazard of children to arsenic. now it's a copper based formula. >> and the problem with the new pressure treatment is not that it's toxic to children, but it increases the corrosion to fasteners, nails and staples and bolts so that if you take the new pressure treated lumber and you nail into it, the nails will deteriorate quickly. quickl