I assume that you have to leave your keyboard unattended or out-of-sight. I guess that if you have audiences with Korg arrangers then this could be a serious issue for you. I would assume that most people would be within sight of their gear and be taking it home at the end of a gig but I know that sometimes this is not practical. I assume that you don't want to power OFF the keyboard?
Did you ever look into the "locking USB" keys? There was an old forum message about these (can't find it now).
Without a password protection option, I assume you need to find a way of rendering the keyboard unusable, or at least, in a very inconvenient state.
I am still amazed that you have audiences comprising Korg PA "SET" thieves. I can't judge because where I am located, not many people even know what a Korg PA is !! (including some retailers

I hope you can find a solution as this is clearly a long standing problem for you.
All the best
Pete
