I just retrieved my anchors after leaving my boat anchored in a river for 4 years with minimal supervision. I had two anchors, one upstream and one down. A Danforth type and a plow, connected to a heavy swivel. After a couple of years the swivel froze and since the swinging wasn't random the chains wound themselves around...and around... and around. I had plenty of scope to start so even at the end it wasn't too short. Just beware that swivels can freeze up.
I should have replaced the swivel but where I am there are none available.
Never, ever! buy Chinese.
Because they're cast, not forged, and they rust, big time.
Don't ask me how I know.