The problem is I have very limited space in my compound for a pond of bigger surface area. So the only choice is to make a deeper pond for more volume. Also, due to Feng Shui...the pond must be below ground level.

Looks like I have to make the wall a bit higher to discourage cats. But I'm also concerned that this will limit the line-of-sight to the water. So the viewing angle will be from directly above only. Has anybody ever encountered problems with cats? And is there any way to stop them from attacking the fish?

In terms of the filter...as CnT mentioned...is it true that a canister filter will only work when the water level is above the top cover? Can anybody verify this? If this is true...I may have to look at other filter options.

Any suggestions? Tks!