Securing Potentiometers

I'm building a speed controller that will have three adjustment pots for frequency and one for voltage. There seems no mechanism for preventing them spinning except friction with the inside of the face plate which is aluminum They are very free spinning but I don't want problems in the future. Suggestions?

Potentiometer
PXL_20230412_202854789.jpg
PXL_20230412_202902643.jpg
 
In case of any doubt and for future reference: The star washer goes between the pot and the rear of the face plate and the nut goes on the threaded bush at the front of the face plate (preferably with a flat dress washer between nut and front face plate).

An alternative to the star washer is a lock washer as shown in this guitar pickguard assembly (note the second, height adjusting nut):

1681334828607.png