If done properly, the first wrap of the string can prevent slipping.
To fasten a string on the string post to prevent slipping, bring the string up the center of the instrument to the post desired.Put string (A) through the hole or slot in the post at (B) to (C); around the upper side of the post (D), and under the string (A) at (B), back again around the string post (D).
Now when you wind the string, it will lock itself against the post.
Information from Gibson USA Owners Manual, pp. 36-37