Brock didn't have a single rock move. All it takes is maybe a potion + repeated Ember! As long as you're Level 10ish and have a backup Pokemon you should be good.I think I remember losing to Brock a few times in Blue and going "eff it" and grinding my Charmander to like level 25. Took forever, it was a bunch of L6 or 7 wild Pokemon lol.
Then I steamrolled his punk ass with a bunch of "Wasn't very effective..." moves. Was so satisfying. Was also able to cruise for a while after that.