The fence, or fences, with gateways (shin-mon) which enclose a shrine. Tama-gaki means 'jewel fence', perhaps meaning 'fence round the treasure (the kami) though the etymology is unclear. In the past the fence was an arbour or simple fence of brushwood surrounding a kami, but stylised versions in wood and stone were developed as elements in shrine architecture. Ise Jingu for example has four fences set close together. Starting from the outermost fence of a shrine and working inwards the usual appellations are: ita-gaki, soto-tama-gaki, uchi-tama-gaki and the inmost fence, mizu-gaki, though different terms may be used at particular shrines.
A Popular Dictionary of Shinto. Brian Bocking.