User blog comment:Morganacharmedfan/questions/@comment-5674726-20121102233500

8. If Merlin is more powerful and he is worried that Morgana will get more powerful or his level why not go after her himself or at least permently strip her powers if thats possible so she could do no more harm like a binding spell.

Maybe he intended to bind her powers permanently when he used the voodoo doll to de-power her, but they came back. It's possible that Morgana and Aithusa spent two years in captivity because it took that long for Morgana to regain control of her magic and escape.