Anyone?

Is the 6 inches or feet? By grassy plants do you mean anything herbaceous, not woody, or do you literally mean looking like grass?

For specific plant suggestions, you might want to ask at the New England forum. Realistically, most any plant will give off a certain amount of debris, but tall grasses or non-running (clumping) bamboo might be a good choice as they tend to hold together relatively well until winter when you aren't using the pool. You should cut them back before spring growth starts. If you are OK with non-grasses, you could grow flowering vines on the fence, such as Clematis. Any debris from petal drop should be far enough away to not end up in the pool, and in my garden the seeds stay attached well until after pool season. Type 3 prune Clematis get cut back to about 1'-2' over the cold season so debris gets removed all at once. Siberian iris have a short growing season, but don't generate much debris in my garden.