on iron island in platinum
in rout 228
down the left staircase in iron island should be there
in iron island
there is 2 one in iron island(room on left when you enter one in the desert in the battle zone(down a bike slope)
Rhydon
I remember finding one south of Vielstone city, but Diamond had it south of Stark Mountain... Perhaps this is because Ryhperior is in the new Sinnoh dex.
Route 228.
If you put it on certain Pokemon and trade it, it will evolve.
A Protecter evolves Rhydon into Rhyperier.
Route 228
If you give it to Rhydon to hold and trade it, it will evolve into Rhyperior.
Route 228 is where you can find a protector.