Detecting debuggers

Let's assume that we're all using an NT based OS (2k, XP, 2003). It's a simple matter to detect that you're being run unde a debugger - simply isue an IsDebuggerPresent call. Heck, you could even put it into a thread that intermittently polls and reacts (in)appropriately.
Of course, I'm not one for polling. Never have been. I just consider it 'lower class' to do something like that. This is of course why I like the next trick for detecting the arrival of a debugger.
what happens is that an external thread attaches and executed the 'DbgUiRemoteBreakin' function; which at some point issues an 'DbgBreakPoint', which of all things contains an int3 and a return statement (this is a kick the debugger operation).
Detecting the debugger consists of rewriting the function implementation.
What we want to do is invoke our function (fun) when a debugger attaches. The following code does just that, and as a result of the attachment of the process simply spits out a message and terminates.

#include <windows.h>
#include <stdio.h>

HANDLE wh;

void
message(void)
{
        SetEvent(wh);
        ExitThread(0);
}

int
main(int argc, char **argv)
{
        unsigned char *abki;
        HMODULE dlh;

        wh = CreateEvent(NULL, FALSE, FALSE, NULL);

        dlh = GetModuleHandle("ntdll.dll");
        abki = (void *)GetProcAddress(dlh, "DbgUiRemoteBreakin");

        if (abki != NULL) {
                DWORD olp;
                if (VirtualProtect(abki, 20, PAGE_EXECUTE_READWRITE, &olp)) {
                        *abki++ = 0xb8; // Mov EAX,
                        *(DWORD *)abki = (DWORD)message;
                        abki+=4;
                        *(WORD *)abki = 0xd0ff; // call EAX
                } else {
                        printf("Page Protection Failed\n");
                        return (1);
                }
        }
        WaitForSingleObject(wh, INFINITE);
        printf("Debugger\n");
        return (0);
}

This is the beginning of something bigger.