Are you talking about a system like a horse walker that usually has 4 extensions of a main pole and swivels? If so they actually have mills like this for a dog but only one extension. They are usually called jenny's or cat mills. As long as you make the chain long enough to touch the ground there shouldnt be any strangulation risk. Also I would never leave them on it unattended.
"Life is like a grindstone. Whether it grinds you down or polishes you up depends on what you are made of."
But a Constitution of Government once changed from Freedom, can never be restored. Liberty, once lost, is lost forever. John Adams