Had a Rival 34 moored fore-and-aft on the Tamar last year, with two 20mm new lines each end, and each chafe-sheathed.
I inspected closely ( and kept an 'insurance log' ) each time I visited, and found that flakes of rust from the summer-new galvanised hard eyes were chewing into the lines where the splice-loop divided and was seized to the eye.
That's when I put on an additional 'loose' chain wound around a car tyre 'snubber'. Inelegant - but effective. The boat was then going nowhere without my prior approval.