Disclaimer: Rhyhorn is almost completely outclassed by Onix because of sturdy and the speed difference. Don't use Rhyhorn unless Rhyhorn is your absolute favorite Pokemon and you'll use it even if it means losing every battle. If you're still set on using Rhyhorn, then use this set.
Rhyhorn @ eviolite
Ability: lightning rod
EVs: 236 HP / 36 Def / 236 SpD
- stealth rock
- rock blast
Switching is common in LC, so stealth rock is necessary for dealing damage. Earthquake is Rhyhorn's main STAB. Rock blast and megahorn cover flying, bug, and ice, and grass, respectively. Rock blast is also good against weak armor Vullaby. The item and EV spread maximize its bulk.
By the way, moveset questions aren't supposed to have best answers.