Planning pond build but have questions

Hi, I'm planning to build a pond part above ground and not sure how to mount filters. There will be about a 15" block wall (about 2 cinder blocks high) and then I will dig down another 24". I'm undecided on a diy skimmer and water fall or to buy them? My problem is how to mount a skimmer to a block wall with it being a level surface all the way around? It will be 12'x5' and around 3' deep.
It will be right next to the house and deck. The steps from the deck is the reason for the short wall because it will be right next to the pond. Hopefully this will keep anyone from stepping onto the pond and could also be used as a seat. I know the skimmer has to be at water level and how can I run the plumbing to hide it? I would like to use something like this http://www.thatpetplace.com/pet/group/11695/product.web and http://www.thatpetplace.com/pet/group/11697/product.web
Will this even be possible for a block wall?

Justbecause, on the top course of your blocks use bricks when you get to the spot for your filter leave the brick out and build it up with mortar to adjust water level. run liner over mortar and into filter. .using bricks around the top will give you a nice edge to hide your liner. rock on rock

I don't understand how you mean to use mortar. Should I leave the top block out or both and mortar from the ground?

is your pond just going to have one level. or more

At first it was going to be one level but I'm thinking that I should have at least one shelf for plants. Will this make a difference?

The plant shelf wont matter . i would forget the skimmer , and put a pump in the pond , pump out to your filter thats above your water level , then gravity feed it back to your pond, Via waterfall . the higher the filter the higher the fall

So I don't have to have a skimmer? That would save a lot of trouble.

Skimmers are a nice to have item. In my 40 years of ponds I have never had one. The most recent filter I have built is a biological filter which keeps the pond crystal clear. I used a 55 gallon drum to build mine with then built my 2nd waterfall around it.

Wow, how often do you have to clean it? Is it hard to maintain and is it inside or outside of the pond?

It is cold now, so I haven't done it for about 6 weeks. When it is warmer and the fish are feeding, I do it about every 2 weeks.

With this filter, all I have to do to clean it is open a 2" dump valve for a couple minutes and the sludge that is trapped in the bottom, backflushes out. Then I close the valve and I'm good for another couple weeks. The plants love the stuff and I don't have to take apart anything.

I have a filter media filter on my other waterfall as well, but I only run the large waterfall on special occasions. That filter must be taken apart and cleaned. It only removes large debries and doesn't do anything to keep the water clear.

The bio filter, once it starts doing its thing will clear the water and keep it that way.