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The best defense is to put it in a location which is energetically repellant to those you consider hostile. My island accepts some types of minor hostile thinking so that tourists can visit, but that's why I hired a demon army to maintain security. I'd suggest setting up the shops first, then hire a manager for a garrison by summoning some decent sentry demon, then let him use a set percent of your income to hire and maintain your security. If you get money over, create an investment account/bank which naturally refines anything stored inside (otherwise it could perish with time). You can either create magic devices that do things, or you can hire someone, a combination is best. I have greys running the administration at my mansion, but I also micro manage some things like the establishment of a restaurant that makes a local traditional food using ingredients I grow outside. The heating for the stove is hellfire I lead through a shaft from a sacrificial hellfire maintained by drow who live under the island I married them.
Remember that you can use "automatic" contracts. That is you define some simple rules and anyone who wants to support you can self-employ themselves by accepting the rules. Make it simple, like they have to accept that their Qi flows through the eco-system of the island and through this, the goods they need to live there will manifest. Aside from that they need to perform a task like security or serving guests, and they can keep 40% of the income, the rest will go to the island account or into the eco-system.
Post the contract on a stone wall using screws made from the same drilling method you used to establish the island and it's visible to everyone and no one can violate the contract after it's formed.