If you already have mending, and you just use your rod only for FISHING, then unbreaking enchantment will be redundant, unless your timing is way too bad.
In order to obtain the highest level of enchantment, you need a total of 15 bookshelves. The bookshelves must be arranged one block away from the enchanting.
An item can be enchanted by using an enchanting table and placing the item in the input slots and uses 1–3 lapis lazuli but can hold up to 64 lapis in its.