Why can't I smash rocks with Rock Smash?

Hey guys I have Pokemon Ruby on GBA and I have a problem. I have obtained rock smash and taught it to one of my Pokemon, but I still can't smash the rocks in the tunnel at Slateport. What might be the issue?
Best Answer
If you haven't beaten Wattson of the Mauville City Gym yet, therein lies the problem. Hidden Machines tend to require that you beat a specific gym before the moves can be used outside of battle, often to get at hidden item balls, or to clear a path forward. It is primarily used in order to keep the player from doing things out of sequence; you cannot proceed to the next town until you have found the HM required to take the path, and beaten the gym leader to unlock it as a field move.
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How do you use Rock Smash to break rocks?
You'll find Rock Smash from a man in Mauville City, but you won't be able to use it outside of battle. In order to use Rock Smash, you'll need to defeat the Gym Leader at the Mauville City Gym and earn the Dynamo Badge.Liz Phair - Why Can't I? (Official Video)
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