I've been thinking about the resource game in the wilderness more, particularly as it related to mercenary casualties. Domains at War provides us with the handy heuristic that half of troop casualties are slain or die on the field, and the other half are lightly wounded. Looking at the Mortal Wounds table's better half, this means they probably need about a week of bed rest to be back in fighting shape (Domains at War glosses over this, but I think it could be useful for our purposes), provided that you have held the field and can retrieve your wounded.
The bar for bed rest in ACKS is something like "complete rest in reasonably sanitary conditions". For a site to be useful for this purpose, 1) you need to be able to defend it without involving the wounded troops - it should be defensible and out of the weather, and 2) the basis of sanitation is access to clean water. You need it for drinking, for cleaning injuries, and for keeping the site itself clean. It's also just nice to have generally to ease logistics and refill.
So some examples of such sites might include:
- Shallow cave complex with a natural spring near the entrance
- Crumbling tower built by the men of the first age, with intact cistern
- Caravanserai near an oasis
- Rivendell, Beorn's homestead, Craster's Keep, and other features defensible by virtue of powerful friendlies.
- A palisaded beastman village with a well, whose inhabitants have been put to the sword
So the system in play would look something like this: you're exploring a hex and you find a crumbling tower overlooking a stream, a refuge with a capacity of say 60 men. Your thief scopes it out and by luck finds it empty, the door locked. You make a note of it on your map and continue forward. After a skirmish with some beastmen, your heavy infantry retinue squad is at half UHP, 3 of 6. This represents about 1 dead and 2 wounded. You hold the field, gather your wounded, and retreat to the refuge, where you put the 2 wounded on bed rest and the rest of the squad on guard. You send your explorer and his light infantry squad out foraging for rations while the heavies heal up. He gets into a random encounter or two, but by good fortune they're just animals and easily dealt with (and eaten). Seven days of rest later, your heavy infantry squad is now at 5 out of 6 UHP and hungry for revenge.
So the tradeoffs here: if you're far from town, you can get some mercenary healing (and PC healing too actually, at 1d3 HP per day of bed rest, more with the Healing proficiency - only relevant if changing the resource model on spells in the wilderness from "per day" to "per adventure"), but you can't refill all the way back up, it'll cost you in rations, and you put yourself at some risk for further random encounters (but a reduced risk compared to going all the way back to town at one roll per hex).
This ties to domain play in a couple of ways:
First, what is good for the goose is good for the gander. Refuges are very attractive sites for monster lairs, and in some cases you might have to "liberate" them from a monster lair to use them at all. A refuge that sits empty is liable to be re-inhabited between expeditions, which might necessitate re-clearing it. This creates an incentive to establish small garrisons, to hold refuges between expeditions. Human presence is likely to keep most animals out of the way, but may not be a deterrent to beastman warbands. A back-and-forth, where a refuge is taken by and re-taken from beastmen, is pretty plausible and good re-use, good for building up campaign capital in a site. Heck, "we're in town and can see a smoke signal from the garrison, let's get all our cavalry together and go relieve them" sounds like a pretty good time.
When you have a garrison, you have to support it, not just by relieving it with cavalry, but also with food. Generally you can only feed about one person per square mile on hunter-gathering (so say 30 men per 6-mile hex, for convenience) under good conditions (ie, not desert, glacier). Conveniently, 30 is also about the size of a beastman warband, which presumably also forages and hunts for its rations (as opposed to a village, which is dense enough that they're probably doing slash-and-burn agriculture). So if you want bigger garrisons that will have better odds against a warband, you need to either lay in supplies (entailing logistics, defending caravans - and with spoilage, this might not be viable at all), or you need on-site agriculture, ie peasants. An amusing intermediate step might be livestock. 30 men eat 30 stone of food a week, provided water. A 550lb cow from the Livestock table yields about 27 stone of meat, probably more total rations if you're willing to boil the bones and such. A cow per platoon per week sounds very reasonable, and they don't spoil - if you want to supply a garrison for a month, give 'em a week of standard rations and three cows. And then you have an incentive to clear predatory-animal lairs that would otherwise be of no interest (dang giant eagles eating your cows), and you can have goblin cattle-rustlers!
Extra rules for butchering livestock provoking random encounter rolls? Herdsman hirelings? Clearly this whole livestock angle is one that could use more detail.
Anyway, another way that refuges lead into domain play is through capacity restrictions. You want to have a garrison strong enough to hold them, but you also want enough space for your retinues to heal. So you're probably going to want to expand the capacity of the refuge. Put up a palisade around your crumbling tower to increase the capacity. Uncrumble it to increase the capacity. Build and consecrate a little shrine so your cleric can get a bonus to RL&L rolls (and maybe even restore his 1st- and 2nd-level spells in the field). A refuge is the raw materials for a base, and players like base-building; so give 'em base-building. Whether this will actually work with ACKSonomics is another question - it's not that construction is hideously expensive in ACKS, it's that labor is hideously unproductive. 3gp/man-month on an unskilled laborer (like a mercenary being employed to build a palisade) means it would take a platoon 40 days to build 100ft of palisade. I suppose if you have a platoon-sized garrison just sitting around that's not totally implausible? Might need some notion of garrison activities - a garrison can be building structures, or hunting and foraging, or patrolling the hex, in addition to holding the refuge, with different risk profiles for each of these activities.
Finally, as a feature on a hex-map placed during stocking, how common should refuges be? I feel like a power law is reasonable - squad- or party-scale refuges, with a capacity of maybe 12, should be pretty common. Almost any lair of large predators, once cleared, can probably suffice. Platoon-scale refuges in the 30-60 capacity range are probably less common, maybe one in every seven hexes (one within a one-hex radius of any point, in expectation). Company-scale refuges you probably have to take from a tough lair like a beastman village, maybe one in 19 hexes (one within a two-hex radius of any point, in expectation).
Bonus: dealing with mercenary casualties as combat ineffectives who need shelter and bed rest also lends itself nicely to disease and exposure. A "trap" in a swamp hex might have characters save to avoid catching disease - mercenary squads who fail their save take some amount of damage temporary damage which can be fixed by bed rest, but if they don't get that bed rest within a certain timeframe, the damage becomes permanent as people die of dysentery.