I use the commercially available colored rubber dogbones that insert inside the link. Defender carries them. I use two for each mark, so I can see it whichever way the chain is oriented, and if one pops out I don't misread the length. I lose about one dogbone a month which is quite acceptable and keep a bag of them in my pocket as I'm pulling up the anchor for rapid remarking if needed. I've used both paint and cable ties in the past and find these dogbones vastly outlive either solution.
Whatever you choose, double the marks so you won't misread the length after a single failure. We dragged at Isleboro once due to misreading the marks and learned this lesson.
s/v Kamaloha - K1QE
1988 Tayana 37 Cutter #542