Rocky also known as Rocky the Rock, was Patrick's "pet" rock whom he had taken for a snail because he wanted to be in the snail race as well in "The Great Snail Race."
055a - The Great Snail Race 205
Rocky looks exactly like Patrick's Rock, but as a smaller version. His first appearance was in "The Great Snail Race" where Patrick entered him to race against Squidward's snail, Snellie, and SpongeBob's Gary. Ironically, Rocky ended up winning the race despite not being an actual snail.