The buildings are occupied because the owner do not live there. Squatters target housings that are left empty by owners who are just speculating on the market.
I personally know a handful of cases where okupas tried to take people's primary residence that they just purchased and were in the process of reforming before moving, for example. And every single case was solved quickly by local police, as it's breaking and entering, not a occupation.
The sprays could be made very difficult to disconnect. A new one would activate each day in a new location. If day 1 spray is disconnected, day 2 would be twice as much volume.
It has been shown on Youtube that fart spray does work for theft, it's time to deploy it as an actual product everywhere.