Chain marker auto clip. Design for a chain of 10 according to DIN standard clip some markers every 5m or whatever you prefer along your Anchor chain. you will alway know the chain lenght in the water.

print by lot of 3 or 4 if you want to avoid overheating during process. Especially if you have a poor part cooling fan.

Of course use water resistant plastic. (ABS, PET...)

Added stronger clip, need to be pressed with a pliers.