Hey there! Your character is free to build/buy/rent/construct a sanctuary of that sort within the City limits, provided that it is played out appropriately, (taking the time to get the resources, not just assembling everything in a week, expansions taking time, etc.). However, keep in mind that if he wards the sanctuary in the manner of his canon, it would still not prevent curses, or prevent people from inside being able to be cursed. It could prevent people from normally doing violence, or prevent people cursed to want to do violence from being able to go through with the full action, but it wouldn't be able to protect people from actually being cursed.

If you have any more questions, let us know!