Elaborate Laboratory Help

If no other magus enters the laboratory, it is irrelevant.

If a maga does enter his laboratory, and this magus kills her, then he just needs to made a case at Tribunal that the marking was adequate and present (if somebody else protests the killing). Whether he can successfully make the case or not will depend on his political skill and the context of the case and Tribunal.

Since I missed CH comment above, I'll expand on yours. Occupied Size is not Size (p 110). You must use the Free Structure Flaw: Empty to cover the unused space (p 114). And yeah, if you cannot keep it clean it's not healthy.

That brings the amusing fact that Refinement increases Safety twice: once by reducing the Occupied Size, twice by both being used for of Base Safety.