The Strong Push Secret Technique is needed in order to move large boulders found across the Kanto Region, effectively replacing HM Strength found in previous Mainstream Pokemon Games. With this technique, you will be able to push any and all large boulders blocking your path during your journey. In order to obtain this Secret Technique, you must first obtain the Gold Teeth from Team Rocket on Route 19 located just south of Fuchsia City (which they will freely give to you). From there, you will need to return the Gold Teeth to the Safari Zone Warden in Fuchsia City. As a thank you gift for finding his teeth, the Warden will teach you the Strong Push Secret Technique.