Submersible Halloween lights allow a wide range of innovative decorating schemes. They can be placed in a water-filled vase and used as a centerpiece, in a pool, or wherever there is water. Or, they can be used out of water. Since they are waterproof, outdoor use is not a problem.
The things I would recommend that you look for include the words battery operated. A battery operated light string does not connect to your electrical supply, so if it does short out the damage is likely to be confined to the string of lights. Another feature that is highly desirable is remote controlled. It can get messy reaching into water to turn lights on or off, especially into a full vase.