I think the big incentive for everything rats do is survival. They know very well when they are not inside my walls and they are outside roaming for food, they are at great risk from predators (like birds and cats). This is why aromatherapy fails. Rats have a highly sensitive sense of smell and so if mint insense or a diffuser of mint oil is running, it’s quite intense for them and is said to be a repellant. But in reality it fails as a repellant because rats will tolerate a lot when the alternative risks death.

I don’t know why my walls are of particular interest, vs the neighbors walls. Maybe the neighbor has a cat. I wonder if I should try running a diffuser with strong odors inside the walls on the off chance that they have a better shelter to choose from. OTOH, I suppose I don’t want moisture from the diffuser accumulating between the walls.

I appreciate the insight. It sounds like no solution then… and I need to do a major renovation before insulating the roof.

I’ve seen two things that seem wrong to me though:…a) rats don’t move stone. They can destroy mortar but even then only if it’s weak from what I know.

Rat teeth never stop growing. They will scrape and chew through concrete along with anything softer than concrete, like mortar. They cannot get through glass and metal. So one technique for patching a hole is to mix concrete with broken glass. The broken glass will stop them. But if they are determined enough they would just attack the next brick. There are many bricks in the wall.