Place coconut in a large shallow baking tray and gently shake to evenly spread coconut. Bake for 5 minutes or until lightly toasted. Remove from oven and leave to cool completely on tray.
Blitz together biscuits and salt in a food processor until a fine crumb is formed. Add in 1 1/2 cups of coconut, caramel and rum (if using) and pulse to combine. Transfer mixture to a medium bowl, cover and refrigerate for 20 minutes or until mixture is firm.
Use clean hands to roll tablespoons of mixture into balls and toss in remaining coconut. Store in an airtight container in the fridge.