Locks that work

Are you not able to fit a ground or wall anchor? It's easy, assuming you are allowed to, and some are seriously chunky. Secure the bikes to that using a recommended heavy chain and lock and/or a couple of the D locks mentioned in this thread (like the Kryptonite NY series).

I hear what you're saying, and thanks for the reply, but it's a rented property and it doesn't seem worth the hassle and expense of getting it done when I'll probably be moving on in a couple of years or so.