Things You'll Need
Instructions
Free Rock Smash
Beat Whitney in the Goldenrod City gym and get a Plainbadge. Whitney fights with two Pokemon, a female level 18 Clefairy and a female level 20 Miltank. You will have an easier time if you bring Pokemon with moves that are super-effective against normal-type Pokemon.
Go northeast from the Goldenrod City gym until you get to the house with the plant-watering lady. If you have the Plainbadge, she will give you a squirt bottle.
Travel to the intersection connecting the routes to Goldenrod, Azalea, and Ecruteak and use the squirt bottle on the tree in the middle. This tree is actually a Sudowoodo, and it will attack you.
Catch the Sudowoodo if you can before making it faint, because it is the only one you will find. If you cannot catch it, simply defeat it. You don't need to catch the Sudowoodo for rock smash.
Walk east down Route 36 until you see a fat man. Talk to him and he gives you TM08 (the TM for rock smash) for getting rid of Sudowoodo free of charge.
Buying Rock Smash
Travel back to Goldenrod City if you have already gotten your free TM08 and you would like to teach rock smash to more than one Pokemon.
Walk into the Goldenrod department store and go up to the fifth floor.
Talk to the vendors there and buy TM08 for 1,000 Pokedollars to teach more of your Pokemon the rock smash technique.
Leave and find trainers to battle in order to raise the money if you do not currently have enough Pokedollars. If you have already defeated all of the trainers in the game, then you will have to battle the Elite Four to earn the money.