I use rings on the turnbuckles, with a ring big enough to go around the turnbuckle body and through the hole on the bolt at each end. They are easier to remove if adjustment is required, and can be re used. Cotter pins can get jammed between the turnbuckle body and bolt, and can be extremely difficult to remove. Cotter pins cannot be re used. A wrap of rigging tape usually prevents the ring from catching on a line and pulling open.