I have a hillside with 5 terraced beds about 4' x 25' and been growing vegetables there for 8 years. Well, the 2X12 pine boards are finally shot and need to be replaced. They were originally supported by metal stakes. I'd like to slightly change the design and would like your input.

The metal stakes are dangerous and have ragged edges from hammering and I'd like to get rid of them for a permenant post. Have you ever noticed the sound barriers on some highways that have the panels fit into slots on vertical supports? I was thinking of making a mold from 2x stock and create that with concrete, kind of like a vertical I-beam. The wood planks would fit in the slots. When the rotted, they could easily be replaced by sliding in a new one. The post wouldn't stick out as far as an exterior timber post, last forever and I think the look would be pretty cool. Kind of the concrete verion of the connectors that you see on those expesive raised beds in catalogs.

My only concern would be the stength of the lip that would be bearing the weight of the dirt. The walls are about 18" tall.

Any ideas for strengthing the concrete at that stress-point or other comments would be appreciated.