Pokémon evolve in various ways in Pokémon Brilliant Diamond and Shining Pearl. Most will evolve just by leveling up, but some require extra steps. Some Pokémon will only evolve if traded while holding a particular item. One such item is the Protector, which will allow your Rhydon to evolve.
In Pokémon Brilliant Diamond and Shining Pearl, you can get the Protector in two locations. The first is on Route 228. It is located up a slope that you can climb with your bicycle at the beginning of the route. The other location is at the Battle Tower, where players can purchase it with Battle Points.
Trading a Rhydon with the Protector is the only way to get a Rhyperior. This rock and ground-type Pokémon is a physical powerhouse and tank which will surely be a boon to any team. All you have to do is have your Rhydon hold the Protector and trade it. Just be sure to have that person trade your Rhyperior back!
As said, this is the only way to get a Rhyperior which you will need to complete your Pokédex. Even if you have no interest in Pokémon, you will need it to 100 percent the game.
For more information on Pokémon, check out Where to find the Electrizer in Pokémon Brilliant Diamond and Shining Pearl and Where to find the King’s Rock in Pokémon Brilliant Diamond and Shining Pearl on Pro Game Guides.