How can I prevent the theft of my watermelons?

I am but a humble watermelon salesman, fourth generation, my great grandfather came to America from China in his youth to start his watermelon selling business and it was a massive success, garnering him notoriety with locals and even up and coming celebrities and models in NY as it is said the fruit has properties that slow aging and promote healing. My grandfather took up the business, then my father who taught me. My father has sadly passed away last April as he got into a fatal accident, his friend who was driving was drunk. Long story short I'm new to this whole endeavor and with them all gone (save my grandfather who has dementia) I have nobody left in the family to go to in order to teach me the ways on watermelon entrepreneurship and what to do about theft or those threatening violence against me. What should I do?
How can I prevent the theft of my watermelons?
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