Remote Desktop : custom gina.dll

I have a pc with enabled Remote Desktop and work on this pc as Administrator.
If another pc connect to this pc as Administrator my session will be
disconnected and the other user can work with my session. I'm searching for a
way that I can confirm or deny this adoption first.
I found no way to do this with standard windows so I decided to write a
custom gina.dll

I take the ginastub from plattform SDK and try to modify it.
And now there's the problem. I found a function called "WlxDisconnectNotify"
but I don't know how to use it.
This is my code in ginastub

VOID WINAPI WlxDisconnectNotify (PVOID pWlxContext)

((PWLX_DISPATCH_VERSION_1_4)Winlogonfkt)->WlxMessageBox( WinlogonHwlx, NULL, L"WlxDisconnectNotify",

GWlxDisconnectNotify (pWlxContext);

I only try to display a messagebox when a session is disconnected. But I
can't see this message box. Is this the wrong place for the messagebox or do
you have any other idee how to solve the problem?