I am thinking you need two pumps, one for your feature and one that actually functions to keep your water clean and oxygenated. The one that cleans the pond maybe can be either pumped back into the pond via hose or the lip of your filter can be level with the top of your water allowing very little ripple effect which can be hidden under flagstone. For the type of set up you are envisioning you would also need a pond air pump with air stones to allow oxygenation.

http://howtotakecareofagoldfish.com/low-oxygen-levels-in-your-goldfish-pond/

http://www.kokosgoldfish.invisionzone.com/forum/index.php?/topic/92363-diy-skippydoc-style-filter-assembly/

Jodie,

What you are wanting to do is going to be very difficult at best. What I would thing of for a skimmer is an Oase Aquaskim with a submersible pump with the output from the pump run with a tube to the other end of the pond under water so you don't see the water movement. That is easily done. The overflow can be just a couple of 1/2" pipes set at the very top of the pond and run to where ever you want. Easily done. The problem is the dripping water off the cement leaves. I would run from the house water supply a setup like what is used in a hook up for an ice maker. I would install a needle valve on this. The problem comes from the amount of water evaporating from the leaves. When water is evaporating faster the drips will slow down or stop and when the evaporation rate slows down the drips will speed up. A pond pump will never keep the drip rate at a constant rate. As far as oxygen in the pond as long as you keep the fish load lower you won't have a problem.
Mike

This is very helpful.
The Oase Aquaskim is an epiphany!
I'm now thinking I might add a runnel in which case the water can flow with a little more authority. I'm after subtlety.
Thanks so much!

Either a submerged or external pump could be used.

To get the water level as high as possible you do have to be careful with the design. Obviously great care in leveling. If you build with epoxy, fiberglass, etc over concrete you can get the water level even with the top of the flagstone. Great look but people tend to fall into the pond.

With EPDM liner you can get the water to the underside of the flag. You really need a concrete collar for that and the liner can't go very far under the flag assuming you'd be using veneer flag (thinnest).

You can use the overflow as the skimmer. It's just a low spot in the collar, no skimmer door needed. You then run a trench in the flag to say under a planter which would contain the skimmer basket. You could flag over the trench or leave it open which is a modern look.

This all depends on a constant water level. No point of going to all this trouble if the water level is always down due to evaporation. To get a constant water lever a second pond is added some place. It can be very far away, even in the back. A submerged pump is kept in the second pond and pumps water into the first pond thru an underground pipe. The first pond overflows into the skimmer and then into the second pond. This keeps the first pond 100% full all the time and enables the skimmer to work without a door. The opening for the skimmer can be very thin, even 3/4". Virtually invisible.

All evaporation shows up in the second pond. So there you put a float valve to add water.

For a still surface you can't have any air pump or obviously any stream. It's a common mistake to think the surface of water has to be broken to get O2. Gas exchange happens right at the surface. If there's no water movement at all O2 will only be in a very thin layer at the surface. That's in lab conditions. In ponds there's always some movement of water even without a pump. As water moves around so does the O2 at the surface. To speed this up we add pumps to increase movement. So here you can just send the pump's output at the bottom. You don't want too large a pump or you'll see surface movement.

The drip deal can come from the same pump as the skimmer. It's the best choice imo. You need need to split the pump's output into 2 pipes. A one to the drip and one going to the pond bottom. Put a valve on the one to the bottom after the split. With the valve wide open no water will go to the drip because it's higher. As you close the valve water will come out the drip pipe. You can adjust to get the exact effect you want. I'd use a gate valve for best control. The valve should be as far away from the pump as possible. Too close and you can get water pushing back into the pump and that just wastes electric.

Resist the temptation to use a small diameter pipe to the drip. It may seem silly to use a 1" or 1.5" pipe for a drip but the pressure needed to push water thru that small pipe is still an issue.

Sounds like a fun project.