The Clothespole is actually fairly easy to break.
Trying to fish on the Selbina-Mhaura Ferry using Sliced Sardines will cause Line breaks and Rod breaks in addition to catching the occasional Gugru Tuna.
If you're looking to get a guaranteed rod break and nothing else, try fishing in North Gustaberg in the cascade with meatballs... anything that is a !!! catch is either a monster you'll have to fight or a Gavial Fish which will break the rod. Anything with a single ! is just an item so they can be canceled.