what are you attaching it to? the easiest way for wood or drywall is a staple gun for sure, although tacks would work with drywall. if its plaster you're on your own
i really think everybody has it backwards. if you are waiting 2-3 days between waterings, i dont think overwatering is the problem (unless you flood it every watering). that being said, do you notice the drooping directly after watering or towards when it needs another watering? if the latter...