Where do you get TM focus punch in Pokemon emerald?

Hi! to get TM01 (Focus Punch) you need a MACH BIKE!! u go to go to Rustboro, then head north until u get to some water... u then need to surf north until you see an island with a beach and LOTS of trees on.. then u go to the north west part until u see a mud slide, then check at the northest part of the area you are in and it should be there.. :D