He means this house is safe because it's built on rock.
3 seconds sound clip from the The Old Dark House (1932) movie soundboard.
You can hear this line at 00:09:45.335 in the DVD version of the movie.
Quote context
[...]
- You might well be afraid. Your time will come. But, it hasn't come yet.
- This house is safe. I know it better than you.
- Morgan!
- He means this house is safe because it's built on rock.
- You will have to stay here. The misfortune is yours not ours.
- No beds, they can't have beds.
- As my sister hints, there are, I'm afraid, no beds.
- That's quite all right. If we can just sit around the fire, that'll be fine.
- I'm not very sure that I want to go to bed myself tonight.
[...]