Protecting a service from termination.

What is the correct way of protecting a service from termination through the
task manager or through a tool like kill.exe? For example, I know that I
can't terminate SpySweeper's service through the taskbar or through the kill
/f command even with administrative rights. I recieve and 'Access Denied'
error. I would like to implement this protection with my service.

Any information on how to accomplish this would be greatly appreciated!