Map Wall?

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Hey I'm finishing up a map with an underground part to it, so the real "ground" starts at Z 30. I'd like the stone perimeter wall to be tall enough so it shows above the real "ground." Is there any way to do this? As far as I can see, the only map variable pertaining to it is "noWall" but that doesn't exactly help . If not, are there any alternatives?

Thanks in advance!

[ahs3]

-set _wallHeight 40

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Thank ya very much