Mini zen garden help?

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.

 

I would think decking boards would be ideal and look better with their grooved side, rather than just plain planks.

Treat any cut edges with a good wood presevative before dropping into the soil.

To avoid any unsightly large wooden posts for securing the frame to, consider using these knock in right angled metal pegs on each corner, inside or outside.
Galvanised Log Roll Pin 25 x 450mm

For your acrylic sheet you will probably need a little support right in the middle as a sheet that size will sag a bit and collect rain water.
Think I might go for some plastic or metal mesh to protect against wildlife, as the acrylic will probably be covered in condensation and block the view more ..?

 

I have no idea what it is but yes I do realise it needs to be accessible and this 'thing' I am planning should be easy enough to remove without needing to be ripped apart. It will just basically be a cover for it so it doesn't look so unsightly.

 

Those pins look perfect for holding it down. As Marley Farley said, it needs to be easy enough to move to they look ideal.

For the acrylic sheet I mean like an acrylic panel? That shouldn't sag should it? Something like this:


I did consider the condensation though and have found no way past that yet. a net or mesh or something would be better but I think it would kind of ruin the look. Also would probably soak the sand a little much.

 

You really need to find out what this is! Why not lift it and look? If it is a septic tank, this would be in your deeds or property agreement. Best thing to do IMO is to place a large pot with nice flowers on top of it thereby hiding it but allowing access.