I have a concrete slab thing in my garden that I think is the lid to a septic tank or something. Anyway, I have an idea to create a little zen garden (just google mini zen garden if you have no idea what they are! Haha!) to cover it and I am looking for help on what sort of wood I should use or how I should treat/paint/varnish the wood. I was planning on using something like decking boards. Will this be suitable? My main concern is that part of the wood will be dug into the ground for stability so I want to know what to do so that the wood in the ground will not rot or something.
The actual little garden will be around 1m by 50cm and I will cover it with a clear acrylic piece of plastic in order to prevent cats etc. going into it.
I have uploaded a kind of 'split through' picture so you, hopefully, have a better idea of what kind of thing I have in mind.
Thanks in advance for any help.