Problem:
People who commit crimes can hide in a vault, and if the vault is under-siege, they can just go to a new vault, rinse and repeat until scents run out.
Most people don't raid a place for the sole purpose of JUSTICE! that is actually defended. Scents are usually just bonus kills if you just happen to find them to a place you were already going to raid, or free kills if their hearth is in a palisade or unprotected.
My suggestions:
1. Increase scent times. They really are quite short. With the window of time to find the scents, to get to the perp's home, to prepare to siege and to actually siege the place, it's very unlikely to actually raid a place in time, unless you have raid supplies piled up.
2. Scent stacking. Basically scents of the same perp and same type stack into one conglomerate of inventory tile. If one of the scents of the make-up die, the scent is lowered by the amount lost.
3. Hearth ashes and "repairing" scents. When a perpetrator moves their hearth fire, a greenish ash is left in the fire's place. It can only be seen if you have scents to the perpetrator that were collected before the ash was left. You can "repair" your scents by left clicking your scent, and right clicking the ash. After a few seconds, the scents power and time will be reset to when they were picked up. Each scent can only be repaired by each ash once. 
You can also left click scents, and right click on the perpetrator, and after a few seconds (perp must not move) the scents will be repaired, just as with the hearth ash.
4. Dead scents. If the scents hit 0 power or run out of time, they leave a dead scent. This cannot track hearth fires, hearth ashes, or the perpetrator, cannot summon and cannot be repaired. More explanation for purpose below.
5. Labelling scents. Pretty self-explanatory. Maybe only you can see what you label the scent. When you see the perpetrator, their hearth or their skeleton with the scent in your inventory, it shows the label like they were memorized or were kin, with a scent icon next to their name, like the banner of being in the same village. If they are memorized or kinned, you can still tell from the scent icon, and maybe with the label shown in parenthesis outside the name? Dead scents still show the label on the person.
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This would make rangering a bit more important, and lets you make a ranger "trail" to perps who go to new villages. With an actual siege system, preferably based upon authority, it would make village hopping a lot more difficult, and would only be really possible by real villages being friends. It'd also make it possible for perpetrators to still be recognized, but only if you carry their scents around (I'd only see this possible if the scent is just recently dead, or if the crime is personal.)
I'm not exactly sure on the fine details, and if/how it should be possible to track to hearth ashes. The problem with repairing scents, is you don't know if you still have scents out. But if you can't do the time, don't do the crime, I guess.
			



