I think the simplest repeating word sentence is using "police". It isn't as impressive since it only employs two meanings rather than three but is much easier to grasp.
Who polices police? Police police.
Police police police police.
But then who polices police police? Police police police.
Police police police police police police.
Who polices police? Police police. Police police police police.
But then who polices police police? Police police police. Police police police police police police.
Repeat ad infinitum. n-Police police (n-1)-police