Yushania maculata or anceps bamboo should fit your needs. They're about 10 - 12 feet tall and form a very nice backdrop in those situations. They do look better with some mid-day shade though.

Cheers, Barrie.

Squinn-
When you say you want to plant a bamboo behind "it," I'm assuming you behind the koi pond, but inside the greenhouse. Also, what are the winter conditions that the bamboo will have to deal with in your Zone, presuming it's inside the greenhouse?

It will be behind the pond, sort of a screen between the pond and the house. The greenhouse is attached to the house, the bamboo would be entirly within the greenhouse. I am in zone 5 but I will be keeping the greenhouse heated through the winter, minimum 65 F.