Use inactive groups to prevent enemy agent activity

[Pine Needle]

You'll notice that the transfer to inactive group order is before (order number) the agent activity like assassinate wizard/leader or steal artifact. So if your group's leaders and possessions have been disclosed to an enemy, you could counterespionage the group the next turn, or you could transfer the group's stuff to an inactive group, and the enemy agents will come up empty.

This obviously builds on the advice to pay attention to order number.

Kingdoms with 5 or more groups can do this much easier than those with 4 groups, of course. Teleport  or fly group also works to get away from agent attacks, but you need artifact, flight or advanced wizards for that.