The filter will be built with a backwash system in order to minimize maintenance (its going to be quite big and would be tiresome to take care of when using regular filtration system).
Rough illustration on the filter :
1. Inlet from pond.. overflow so the pond surface will be clean from film and trash.
2. Filter chambers. Some will be accordingly filled with brush, ceramic rings, bio balls, filter mat, sponge and filter floss.
3. Backwash drains (controled by individual valves)
4. Overflow drain, controlling water level at constant height.
5. Return line.
Building this way is not only cheaper (compared to factory built pressurized or canister system) but proved long lasting and very effective as well, even in koi ponds where the dirt and poop is much more than of an aquascape. With a simple turn of drain valve, backwashing is done and the clogged filter will be restored significantly hence reducing the frequency of filter maintenance.