A doukake gomu is a useful little helper to slip over your doukake. It helps to keep your arm from slipping and shifting on the doukake during play. Very useful when you got to wear long sleeves in winter and need some extra grip!
The doukake gomu is shaped like a loop and has a rubber band on its back side. Simply take off the doukake from your shamisen’s dou, slide the doukake gomu over and place it where you put down your arm and reattach the doukake.