stockade, fence, weir, entwine around
柵 centers on a barrier made of upright stakes or intertwined materials: a stockade, fence, or weir. The idea of entwining around extends this to things that enclose or trap like a fence.
柵 combines 木 (tree, wood) with 冊, which likely contributes the sound and suggests a row of wooden stakes or a fence-like structure.
The left side is a tree 木, and the right side 冊 looks like a row of slats or stakes. Picture a wooden fence made of upright stakes tied together.
For サク, imagine a sack of wooden stakes used to build a stockade: sack -> サク, and the wood 木 becomes a fence.