should I contain my hugelkulture?

what I mean is - I have the beginning - the logs - laying on top of soil mixed with wood chips.
I am wondering if I should build it in an open wooden box, or otherwise contain it.
The reason is- I am thinking of all these lovely nutrients that will accumulate over the years disappearing into the soil?
Am I wrong?

(probably)

thank you.

The rotting wood becomes a nutrient sink. I don't think you will need to contain it. With rain worms, fungi and other organisms moving nutrient about, it's unlikely that any attempt at containment would be effective. The conditions inside your mound, are well-suited to storing and keeping the nutrients there.

No because it is a nuissance. YOu will have weeds and grass growing there and it grows exactly where the wood is. It is a fashion these days to treat beds like oversized pots and most gardeners start by building something. These beds surroundings are really unnecessary and only cost money. And you won't lose less nutrients because it would not be not water tight so the water with the nutrients simply runs underneath your structure.

No, don't put in borders. They are a pain. You will end up weeding the border instead of doing productive gardening.