Keep a close eye on your built-in indoor cactus garden for any signs of pests such as mealybugs, scale insects, or spider mites. These pests can cause damage to your cacti if left untreated. If you notice any infestation, isolate the affected plants and treat them with an appropriate insecticidal soap or neem oil. Regularly inspect your cacti to catch any pest problems early and prevent them from spreading.