[PvK]

Yes, spies and scouts are a good way, and viewing combat replays is another. Note that if you have a scout in a province where other people are fighting, you get to watch the battle replay there, and the victim may tend to suspect his opponent if a battle is followed the next turn by attacks like Mind Hunt. If you look at the troops remaining in the last battle in a province, you can see who will probably be in there when your Mind Hunt will strike (assuming no other magic happens in between).

Other basic safety deductive techniques include using Mind Hunt against enemies who generally don't have astral mages, and attacking forces beseiged inside a castle (and when they run out of leaders, they'll rout when stormed).

Like assassination and other sneaky attacks, Mind Hunt can win a battle by removing an enemy commander as his force is moving to combat, so that the troops he was leading get left behind and an enemy army arrives at the battle incomplete...