I'm not sure how to handle searching a hex that contains no monster lairs, which is rather likely in Civilized or Borderlands areas. I ran into this while playtesting the Searching for Lairs rules on page 5 of the sneak preview. I used the abstract system instead of mapping, and the hex in question is Borderlands Woods.
The party began exploring the hex. They were relatively unencumbered and had a base wilderness movement of 24 miles per day, or 16 miles per day in woods. This gave them a throw of 17+ to find a monster lair, or 13+ since a member of the party has the Tracking proficiency.
After four hours and a few close calls with wandering monsters they scored their first success. Normally, this would mean they find a monster lair. With zero lairs to be found, I decided this meant they had determined the hex contains no monster lairs at all. This is a very large amount of land to survey in four hours, and if they'd been lucky they could have rolled a success after the first hour. Should there be a minimum amount of time required to be certain that a hex is free of lairs?
As I wrote this, something else occured to me: perhaps the party must succeed a number of times equal to the maximum number of potential lairs. In a Borderlands Woods hex (1d3-2 lairs), they might be required to roll at least one success to be certain it is clear. In the deep Wilderness Jungle (2d8 lairs), they might need 16 successes. This doesn't address the issue above, but seems interesting. Thoughts?
I think there’s a more general question here, which is, how does a party know when they have found every lair in a hex?
If there’s only one lair in a hex, and they find it in one throw, are they aware that it was the only lair in the hex? If so, how?
Having only skimmed the sneak preview at this point, I’m not sure if this was addressed. My gut is perhaps a preliminary stage where the adventurers do some quick scouting just for tracks and the like, and spend some time to figure out how many lairs are in the hex.
Then they can keep track and know when they’re done. Or, if there are zero lairs, be done as soon as they figure out there are zero.
One way of dealing with it is to divide each hex into a number of sections equal to the maximum number of lairs in the hex. After passing the roll, the party is told whether the section has a lair or not.
That still leaves what to do with hexes with a maximum lairs of 0. Perhaps just require the party to visit the hex to ensure there are no non-lair impediments such as dungeons?