Does the opponent not control the ability, then? I assumed controlling the turn entailed controlling all optional actions such as a Zorb activation.
They control your turn, and just that.
All controlling your turn means is that they make decissions for you. However, you still control the abilities, even though they make the descision for you to use it.
So, if they decide to activate your Zorb for your, you still control the Zorb activation. Your Sacred Ground won't trigger.