[Bluepete]

I'd suggest having a chat with the landlord and asking very nicely if you can install a bolt down anchor, there are plenty out there. If it's put close to the wall, it'll be out of the way and the bike will become it's own guard against attack on the actual anchor.

All you would need is a drill and decent bit.

Good luck and if you get permission, give me a shout, I've got the tools needed.

Pete