Good naming convention for private member functions in C++?

For members, I use

//.......vv
SomeType m_XXX;
//.......^^

I'd love to use _ as a prefix for member functions, but names starting with _ or __ are reserved and should not be used.

My idea is, that when I have:

SomeClass myObject;
myObject.[XXX]

when the user (of the lib) write the dot (.), to see all functions (one after another) that are only public.

Is there a common naming convention for this?

_{I know, that I can use pImpl or inheritance, with interface and implementation classes}