HI Stella,
One thing I have seen done, is the building of a rock wall with gaps in it, a wee way out from the back of the structure. This was back filled with gravel and peat etc and then the plants put in and over filled with more gravel to stop peat coming up thru top( this might not be such a problem for you). Then the plants were contained but could still filter and feed thru the gaps in the wall, yet couldnt invade the space either. They did however fill in the gap behind the "wall". Does that make sense. Anyway I have also seen it done with bricks with holes or gaps with great effect.
I am not sure how wide your tank is but on a smaller scale doing something like this might mean that you can have more "invasive " plants.
The other thing to consider, at the risk of undoing all the common sense I have just written, and whilst not aquatic or native is the range of Mondo grasses... some of which will tolerate paladial conditions and you can mix and match for colour and will also over hang..but to that end you could also use Iris's...lol
Navarre