Here, cheaper than a liner and just as effective.
It'll get rid of that "swimming pool blue" look.
I've used this a couple of times on pre-existing concrete work and was pleased with the ease of application and with the overall result. Round pools are a pain for liners due to the large number of "pleats" needed to achieve a circle. This product is flexible when cured, and also has the added bonus that it permanently seals any cracks that you may have in the concrete. Fish-safe, as well.
The poster Crsublette posted this just the other day, that might solve your "waterfall" question. I think it would be a better idea to use this rather than a waterfall, given the formal look of your "pond" (which to me more resembles a lily pool).
There is an unlimited variety of earthenware pots, urns, jugs, whatever. Reference crsublette's post for filling this structure with filtering material.
Using this idea would also give you the ability to incorporate a semi-permanent (and virtually maintenance-free) filter system.
Something similar to this could sit on top of a series of a series of interconnected milk crates. You could cut out the sides of some of the milk crates in order to house the pump and pre-filter while still achieving your desire to filter, but not to see the mechanical aspect of the design. Put flagstone on top of the milk-carton matrix to hide the tops.
Most of these planters already have a drainage hole in the bottom, so sticking a black PVC pipe up the middle of it, connecting it to hose through the milk-carton matrix, connecting it to the pump/pre-filter and filling it with lava rock shouldn't present any great problems. That's why the milk-carton matrix idea is a good one, You need to support the weight. You can connect 4 milk cartons together using black zip-ties.
I would recommend using flexible sump pump hose for the connection between the black outflow pipe in the decorative container and the pump. Ease of access to the pump is important. You don't want to have to take the whole thing apart just to be able to access the pump. By using sump pump hose (which is cheap and very flexible), you'd be able to wade into the lily pool, reach under the milk carton matrix and pull out the pump/pre-filter combo without needed to disturb the decorative vase/filter.
The sides of the milk crate matrix could be hidden with natural stone. Why go to the expense of a mason, when all you're trying to achieve is to hide the milk-carton matrix? Milk cartons come in black, the epoxy coating is black......
Incorporate at least one underwater light to accentuate the fountain feature.
BE SURE THAT YOU HAVE A GROUND FAULT CIRCUIT INTERRUPTOR (GCFI).
To keep algae at bay, I would suggest adding a dye to the water, and planting water lilies to decrease the open surface area.
Due to the flat, smooth bottom and near vertical sides of your circular lily pool, you might want to invest in an Oase PondoVac4 system. Cleaning your pond would be an absolute snap with this equipment. Not cheap, but you'd only have to buy it once and there is no better design on the market.
There is a motion-activated sprinkler available. Deer are fairly skittish and this might be a good choice. However, if this pond/pool is in your front courtyard........it might work just as well on in-laws.
