I had this idea on the General section of the forum for them, thought it might be good for the BM rework when it comes!
Perhaps BM could create Herdstones in forest areas like you could create Forts/Watchtowers in old TW games, and they are hidden as if in Hidden Encampment stance (but harder to detect), though very expensive to erect new ones. They might function like a psuedo-city, and allow for recruitment of armies etc and have a garrison. The herdstone garrison could have a chance to ambush people assaulting it or going past it, BM are territorial and wouldn't just sit still for an attack on a Herdstone, and would balance their not having walls.
Maybe if you lose all your armies your herdstones become visable or something, so you can be hunted to death, but it will stop you from losing the game if you lose your armies.
It would also stop the AI from just suiciding as BM all the time, and may allow them to establish themselves as a significant threat if you don't root their herdstones out (perhaps they can recruit in a radius or hide armies around them too, so players can't tell where the stones are from where armies appear).
Just a thought anyway.