Generally a year + is the time it takes juveniles to mature enough to were their ready to mate. Cant say for sure if this is what yours are doing ( stirring sand is not an indicator of mateing but nothing unnusual either ) but they typically find something to host ( if not an anemone, then coral, heater, any feature they consider safe ) and make it their home while they lay down eggs and protect them untill they are free swimming.
Should be fine to move the rocks to see if they will find a more visable place to hang.