I don't really have a specific suggestion, since I am definitely not in your area, but I do know that you have much to choose from being in that blessed climate.

BUT, the only plant that does not litter is a PLASTIC one. Don't believe anyone who tells you otherwise. Really, you have to think about the type and timing of the litter rather than just the quantity.

In that respect, most of your more tropical-looking plants produce fewer large pieces of litter that may be easier to scoop out of the pool than small leaves and cones (of Podocarpus, for example). Then again, many of your large-leaved plants would not create the type of barrier you desire...

Just some food for thought... And my oft-repeated advice to check some other forums on this site that actually get some traffic, since this particular one is pretty dead...

I planted Podocarpus henkelii along along one side of my lot and my neighbor planted Podocarpus gracilior and I noticed her plants grew a lot faster than the henkelii, so when they started building a house along my back lot, I decided to go with the gracilior and am much happier with their speed in growth. They are soft leaved also, moreso than the henklii and also a lighter green. I planted them 4 feet apart which is somewhat close but I wanted privacy quickly. I started with 15g two years ago and they are about 10 - 12 feet tall now. This is the first year I did some pruning in front as I want them to grow wider than round.