Looking for Advice with Garden Bed and Garden Edging with Sleepers

During my holidays I am planning to put in a garden bed at the end of the lawn area in the attached picture. I have tried to shade red the intended area. It will be about 1200 deep and 2 x 200 sleepers high. I was planning to use H4 treated pine, either 200 x 2400 or 200 x 3000. As it is quite a long run, I was thinking of pinning the bottom row of sleepers in place by drilling a hole from the top and hammering down a piece of reo bar. The grey stuff you see at the back of the lawn is an old tennis court. It is made up of fine gravel on the top layer and then a layer about 100mm deep of very large gravel that has a bit of bitumen holding it together. It drains quite freely but I will still rip it up a bit with a crow bar in the garden bed to make sure the drainage is adequate. We're planning to use some decking oil on the outside of the sleepers to stain a darker colour.



The garden edging will be to replace that black plastic edging you can see running along the right hand side of the photo between the lawn and the garden. I am looking to use H4 200 x 2400 sleepers, single height. Aslo looking to "pin" these by drilling a hole fron the top and hammering through a piece of reo.



I looking for advice/thoughts on the following -

1. any steps I can take to minimise warping and twisting with the sleepers


2. was considering either stapling some plastic sheet to the inside sides or a couple of coats of outdoor paint on the inside to extend the life of the sleepers


3. any methods of fixing the sleepers together that people have found better than others


4. any other tips before I start ordering materials

2014-11-01 16_00_59-2014 - 1.jpg



Cheers,



UM

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