(Q) How to protect C-functions from being redefined?

["Maciej Maczynski" <macmac@...>]

Hello,

I have C-function registered with lua_register.
How can I protect them from being re-defined in Lua code?
I've tried the piece of code from FAQ, but it seems to be working only with
native Lua functions.

Can someone give me a hint?
Regards,

Maciej