Security on a beach after sundown is normally a function of how many people are around. If the party is all close to the restaurant you choose, and doesn't go walking off down the beach, I wouldn't think you would need to have security concerns. But I suppose maybe someone on island would know a private security guard you could hire for the evening? If your question has to do with Dreams specifically, I've never been there at night, so don't know if Bruno has private security at night or not. I kind of doubt it, but you could ask.