Column re-ordering – How to store the column order?

I am designing a table that enables user to re-arrange the columns according to user's preference. Below is a simple example to demonstrate.

There is a default column arrangement (A-F) but users are allowed to re-order since there are various roles using the table for different interest/ activity. And the idea is for the system to remember the new arrangement so user doesn't have to re-order the columns every time they log into the system.

Currently, I plan to add a lock or freeze table/columns button at C. So it will lock the preference and disable the re-arrange function. Is there any other ways to lock the columns?