Raised beds

I built short raised beds of wood shortly after we moved here, and though the wood is largely gone the piles of soil aren't that tough to keep more or less corralled. Since bending over is getting a smidgeon harder, I built a trial "higher" raised bed, so that the soil is about 20" above the yard. This also let us grow things that want deeper roots--the yard's "topsoil" is about 5" deep and then hits glacial till. Carrots bifurcate or go sideways.

Anyhow, I wondered how long the high raised bed would last and now I know--about 5-6 years. I'm thinking of replacing the useless wood with cement blocks--the 4x8x16 variety, in hopes that the 4" thickness and construction adhesive would be enough to anchor one side wall to the next. I'd dig a little foundation, and then use 3 courses of bricks glued together.

Does anybody have any experience with this? Alternatives? Suggestions? "Round" off the corners?