Much like clownfish taking to an anemone, cardinalfish love to hang out in long spine sea urchins. The urchins provide plenty of protection from predators, but at the same time the urchins present a huge danger in the marine aquarium. The spines can easily break the skin, often leaving bits of black material in the wound. To provide the cardinalfish with their usual home, but without the threat, hobbyists can create a makeshift urchin out of black zip ties. Simply fashion the zip ties to a rock, piece of PVC, or whatever else that will sink, making sure to point the zip ties toward the sky. The fake urchin may not draw in the cardinalfish right away, but they will surely get populated after a while. These plastic urchins are also great for baby cardinalfish, as they will readily take to anything resembling a natural form of protection.