I have never heard/read of such a fig-pit. My taking on that, is that the enclosing
walls will need to be very 'tight ' in order for the roots not break loose (good luck!),
but that may produce a very undesirable swamp fig condition. I have heard of
something similar, but on the contrary, used to improve drainage... I think that
your best bet to keep a fig on the smaller size is to pot it, but that will require more
care, e.g., watering. More heavy pruning will still also keep it in check, if you
just choose to plant in ground.
George (NJ).