I always freak out when we have a small to medium earthquake. Have actually told my boss I am headed home to see if there is 180 gallons of water in my living room before.
The idea of a rock falling over and breaking the glass is what troubles me.
Another thing that haunts me, is a seal on my canister filter breaking. I could come home to find almost half the water pumped out of the tank, and onto the floor.
Damn those canister filters! They do such a good job at keeping the tank clean though.