I do like the look of the English pine used ones. I like the "character"
of them, not worried about creosote leaking or tar for that matter.
I have attached a photo taken about a year ago while I was still establishing
the lawn. The whole garden looks nice now. We have perennials coming on and
as you can see the sleepers look nice and add to the character.
Your sleeper wall fits firmly & naturally between the tree and hedge,
creating a solid, long lasting raised bed for perennials. Simple !