I would build a pergola structure along the entire back area with the apartments behind.......You can plant the top of the pergola with a vine for further privacy.......

I suggest something that is permanent enough to be long lasting and temporary enough to remove at your leisure. It lends itself to your modern exterior and comes in many complimentary colours. I'm suggesting two angled shade sails that overlap to allow directed sunlight while obstructing the neighboring properties view of your yard. They can create effective shadowing, and still allow enough light in to be outdoors. It may well extend tour alfresco beyond your paving, and encourage you to use your yard.
Shade sail installers provide design for your specific needs. They will protect you and your plants from uv, and still allow perfect ventilation.

I would suggest a good tall growing clumping bamboo.

I second seabreeze27's suggestion of clumping bamboo. 'Slender Weavers' variety is said to be brilliant for screening and will help to cool down the yard.

Hi. Have you considered decorative screening ? Blocks the view, let's in the light and adds interest and depth to the landscaping .

I could'nt agree more in regard to the bamboo with a drip system to water it. It grows before your eyes. We planted ours last September and it has already trebled in height. Ours Grows to 4 metres and will be 2 m wide. You only need to buy small ones.

@ Lesley - What kind of bamboo did you plant? The "Slender Weavers" suggested by Nancy or another variety?

Bamboo creates a delightful rustle when there is a small breeze and provides lovely cover. Be cautious however if you go for bamboo that it is 'contained'. Some varieties propagate very quickly and you may find shoots growing up all over your garden. Even meters away from where the bamboos are planted. A solution is to plant the bamboo in the ground with a special very heavy type plastic field around it, which stops the rhizomes from spreading out. We retroactively added this around our bamboos and it is working. Was a lot harder to dig a meter down after they had been planted.

Pittosporum are great and not to heavy.

We bought the bamboo in 20cm pots. Fargesia "Fortune" I think about $30 a pot . They grew over a metre in the first year (we live in Bright in N.E Victoria - a cool climate). This year we expect a 1 and a half metre growth for those in dappled sun - less in full sun. Some say they grow 90cm wide while others say 2m. If you put down a border you can restrict their width. Ours are also very bushy at the base.

"A superb architectural plant. Fargesia bamboo are clump forming and non-invasive, they are regarded as one the hardiest forms of bamboo, they can be grown in containers or planted as a screen. If so a root barrier will help the keep a narrow shape. Very adaptable to most conditions, thrive best in part shade with dappled sunlight but will cope with full sun, although the foliage may curl a little if exposed to this heat for long periods. Fargesia bamboo love plenty of water and organic fertiliser. . Growing to 3-4mt tall and 70-90cm wide." (description from an online nursery)

I also agree with Pittosporum. My late father was a very keen gardener and used these as privacy fencing with great effect.

@ Lesley - Thanks for the info!

I had the east same problem... My small courtyard overlooked by 3 floors of units block. I planted the clumping bamboo Gracilis (I believe it is also known as slender weaver in other states). It grew quickly, screened out the neighbors and looked great. No problems with it taking over or shooting elsewhere in the garden.