I actually carry two spools.
One has only 6M of line on it and is permanently attached to my SMB, main purpose for safety stop marker if I am not coming up the anchor line, although I sometimes shoot it on an anchor line if I want the boat handler to know I am coming up and have my coffee ready
The other spool has 30M of line and is in my BC pocket for other uses. If I have to shoot my SMB from below 6M then I use this one attached to the other and I also have a physical marker when I reach 6M
One has only 6M of line on it and is permanently attached to my SMB, main purpose for safety stop marker if I am not coming up the anchor line, although I sometimes shoot it on an anchor line if I want the boat handler to know I am coming up and have my coffee ready
The other spool has 30M of line and is in my BC pocket for other uses. If I have to shoot my SMB from below 6M then I use this one attached to the other and I also have a physical marker when I reach 6M