To prevent someone from secretly tracking your iPhone, follow these steps without their knowledge:
1. Open "Settings" and tap "Privacy."
2. Click on "Location Services" and disable it for every app or select specific apps.
3. Go back to "Privacy" and disable "Share My Location" in "Location Services."
4. Regularly check for suspicious activity and remove any unknown apps or profiles.
Remember, protecting your privacy is essential. Keep your iPhone secure to prevent unauthorized tracking.