When you install a shackle, it is important that you seize the bolt so that it doesn't come unscrewed and fail. This is very easy to do, all you need is a little piece of stainless steel wire.
The wire is passed through the little hole in the bolt and then around the shackle. Then the tails are twisted together tightly and bent over to prevent snagging on anything. It is always a good idea to tuck the twisted tails close to the bow that way they are less likely to snag on anything.
That's all there is to it! Now make sure that your anchors shackles are all seized up so you don't lose them because a simple pin came unscrewed.