How I think Main Patruls- feature should work
A patrul- function is essentional. Not only for player but also for AI. But there is a big problem with it and it´s the number of lords available after some deaths etc. If AI utilize lords and parties-spots to protect their fiefs there are few left to wage war!
I think patruls should be something the owner of a fief initiates from the fief management screen. It spawns "manhunter"- parties protecting it´s demesne. It´s upkeep is a "Daily Militia" malus and a low maintenance cost. From the fief management screen, player can set how big these parties is. Manhunters counts as militia and count towards "Retires"- malus + an extra -1 "Manhunters" towards militia-growth.
Manhunters has similar but opposite to bandit- behavior. They has their own troop-trees(T2-T4), not very unlike caravan-troops for speed. They are listed as manhunter/patrul-parties. The player can assign the governor to lead these parties if he wants to(of cause with the risk of beeing captives). Othervice they are led by a T5 Sherif, simelar to "Caravanleaders" or "Bandit boss" - semi-characters. They excell when interfeering in battles villigeras and caravans are defending part in. They can't destroy hideouts. They priorities bandits over enemy factionmembers but does not heisitate to join a village milita during raid if they see a good chanse to win. THey can't take non-troop prisoners och don't loot.
A big bonus if player can invest in these parties, above default quality which is based on security and quantity from prosperity, as a way to get also weak holdings on the foot again.
If such party is destroyed, no new patrul can be dispatched for a week. During this week, the holding has another -1 to militia growth.