In Pokémon Emerald, the strongest fishing rod you can obtain is the Good Rod, which you receive after defeating the Elite Four and becoming the Champion. This rod allows you to catch a wider variety of Pokémon than the Old Rod.
However, if you're looking to catch rare Pokémon in Emerald, there are a few things you can do:
* Use the Old Rod in specific locations: Certain locations in Emerald have a higher chance of encountering rare Pokémon, even with the Old Rod. For example, try fishing in the Safari Zone or on Route 124.
* Use a Super Rod cheat: While not technically obtaining a Super Rod, you can use a cheat code to use the Super Rod's functionality. This can be done with tools like Action Replay or Gameshark.
* Trade for a Super Rod: If you have a copy of a later game that features the Super Rod, you can trade it to your Emerald game through a Nintendo DS or 3DS.
Remember, cheating can make the game less enjoyable for some players, so use it at your own discretion.