Article continues below advertisementOK! can reveal Prince Harry and Meghan Markle, 43, are being urged to prepare for heightened security as they head to Australia, with insiders warning their visit could attract protests and unpredictable public reactions.The Duke and Duchess of Sussex are set to travel Down Under for a series of private, business and philanthropic engagements, marking their first return to the country since their widely celebrated 2018 royal tour shortly after their wedding.