What's the chance that smashing a rock in Granite Cave (in Emerald version) will reveal a wild Pokemon (versus the chance of nothing happening)?
>Unlike using Sweet Scent in a patch of grass, there is no way to ensure an encounter while using Rock Smash, and the latter seems to give encounters at a rate of approximately 10% of the time.
Source: Smogon
Note that it says approximately meaning it's not completely a 10% chance.