Water iris. But not the invasive yellow flag.

My day lilies get very tall and are beautiful spring thru fall. One of those old man trees that you can shape as they grow.. I'm not fond of bamboo cause it tends to get wild and overgrows everything.

Would the neighbor let you paint it? Or, can you conceal it with a trellis and then have roses, honeysuckle, paniculata climb vertically. You would not even have to attach it to the wall - sink some posts in on your side

Thanks everyone! Does water iris grow out of water? There is drip irrigation running behind the pond, but they wouldn't be planted in th pond.

Thought of a trellis or pergola, but it's so close to the pond I'm paranoid of a post puncturing the pond liner.

But at least we could build it 2' higher than the wall to block the neighbors driveway.

Know of any vines that don't drop leaves?

Bamboo drops litter like crazy.

Trellis with vine is your best bet. You don't have to put the trellis in the ground--you can attach one to the wall. An alternative would be to add a wrought iron "fence topper" to the wall and plant the vine to one side of the ponds such that it goes up the wall in one spot and only fills in on the "fence topper". Trachelospermum jasminoides is what I would use--ALL plants drop foliage, but it's reasonably clean as plants go and the root system won't be a problem for your liner as Bamboo would be. It is slow to start--sits and does nothing the first year--but after that grows fast and gives a nice screen with dainty fragrant flowers just at this time of spring.

bugh,
Paint the wall either dark green or the color of the stones in the pond.
What ever you planted there, you will regret, it will limit your access for maintance, and you will have to maintain that too.
It'll look nice, try paint.
You have nothing to loose, you could always plant something anyway.

What about starting a line of small arborvitae's and let them grow into place. Their root system are fairly shallow and shouldn't upset the liner.

Craig

Here's another option, coming from a sign guy... ;-)
You could contact a local sign shop and have a large digital print of any high resolution, large format photograph and apply it to the wall. There are several types of material that are specially formulated to stick to brick and concrete walls.You could have a long view of a lake, mountains, forest, even an undersea mural. Just one more option for you that most people don't think about....

Thanks so much for all of the advice! Butterfly, I already regret that the builders put the pond so close to the wall!
The bermuda and nut grass love it back there though. >:-(

The mural /photograph sounds interesting too...it would go with the 8'x8' of Boris Karloff in "Bride" that is on my dining room wall...he's relaxing between takes with a cup of tea and a cig...:-)

Be very careful about grass and bambo I redid my spill way and a couple months later I was tearing my hair out trying to figure where the leak was I had one of the ornamental grasses coming up through the liner in the newly rebuilt waterfall all that nice freshly turned moist soil was a magnet for the runners

I don't suggest planting bamboo because it takes over like a weed. Even when potted, it spreads and the only way to control it is to move.

Have you looked at growing morning glory or clematis? They're vines that are super easy to maintain.