You can catch it in the Resort Area. PS: It appears at differents times. So be on the lookout!
You can encounter a Rhydon on Victory Road on the first floor. A trainer on victory road will also have a Rhydon in his party.
The evolved form of Rhyhorn is Rhydon
You have to trade it while holding a proctector item.
You need to evolve Rhydon. Rhydon evolves when you trade it when it holds a Protector. You find a Protector on Iron Island and Route 228. See related link on details on where to find Rhydon.
You can't find rhydon on a map or room so you must get a rhyhorn then train it to level 42 to get rhydon. You can find rhyhorn on certain rooms like FireredAddamsPokemonMansion.
You cannot find rhypierier on Pokemon Platinum. You have to trade rhydon while it's holding the protector.
you can find one in victory road.
Rhydon evolves when the "Protector" is held and the Pokemon is traded.
You can encounter a Rhydon on Victory Road on the first floor. A trainer on victory road will also have a Rhydon in his party.
you can find millions of geodude in caves and onix gravler and also rhydon
Trade it with the Protector on it
At M.T Stark
You have to get the Moon stone.
to evolve rhydon you need a protector. I think you can get one on stark mountain. Then you have to give it to Rhydon and trade with a friend.
The evolved form of Rhyhorn is Rhydon
Trade Rhydon while it holds this to get a Rhyperior
you give rhydon the protector then you trade him to a friend then get the friend to trade him back and you have your self a rhyperior