You cant catch it in the wild.
But there is one way of getting it.
Its simple; want a rhydon? Then you need a Bonsly!
If you go to serebii.net - Heart GoldSoul Silver - In-Game trades
Scroll down the page and you will se that you can trade with Brock!
Give him a Bonsly and he will give you a Rhydon!
NOTE: Brock is not there at all times! Read at the page on Serebii!
In SoulSilver, you can only get Rhydon in the Safari zone
You can find 1 at stark mountain.
you can find some in victory road
You can't do it in ruby. You can only do it on diamond, pearl, platinum, heartgold, soulsilver, and any others after that!
you can evolve rydon by trading with the protctor
No, you cannot catch Kyogre in "Pokémon SoulSilver."
You can't catch bastiodon in Pokemon soulsilver.
No, you can not catch Phanpy in SoulSilver. It is a version exclusive to HeartGold.
You cannot catch Heatran in Pokémon SoulSilver, you will have to trade for it.
catch a rydon at the safari zone and level up to 42.
catch it? no.
Rhydon's dont hold the Protecter. Rhyhorn's do. They are found in the Victory Road. If you are playing HeartGold you will run into alot of Donphan's first. On SoulSilver it's alot easier. Source's: Serebii.net and I caught a Rhyhorn myself it's a Rhyperior now.