Simple fix to STRING DUPER (Pre - 1.21.3)
IF YOUR STRING BREAKS WHEN YOU SHEAR IT, THAT MEANS IT WILL NOT WORK. THERE IS NO PATCH TO THAT ISSUE. (Versions 1.21.3 and above, this will not work. Also will not work in Forge and possibly other mod loaders)
MOST SERVER SOFTWARES IT WILL NOT WORK ON - (Paper, Spigot, Bukkit ect.)
I hope this helps you fix your string duper and become an economic superpower on your world/server. This took a while to figure out so please let me know if this helped YOU in the comments. Have good day! :)
EDIT - String dupers no longer work on the latest versions of minecraft, Mojang patched it