Nerf or rework rockfall effect?

[valzargaming]

https://github.com/VZGCoders/Pocket-Stronghold-13/blob/840f26a46a67cb65a2705c285b07baffd6976c7f/dwarfs/code/mobs/troll.dm#L48

A issue that has been noticed during low pop hours is that dwarves can be mining and spawn a troll, fight the troll slowly over time, and the troll can effectively destroy a decent portion of a fortress until it is dealt with. I'm unsure what the best resolution would be to approach this. So far I've come up with the following possible options:

• Nerf the probability rate (Easiest, least expensive)
• Scale the probability rate based on the number of dwarves nearby (Easy, expensive)
• Limit what types of turf where rockfall can occur (Most expensive)'

Are there any other ideas or recommendations?