I've been trying to find/negotiate a place for my barrel filter, but there
really are not any good options.

But I realized that the basement entryway is only about 15' from the pond.
This is basically a 8x4 concrete room where the outside stairs turn to meet
the basement entry door. It even has it's own drain. This is where I ran the
electrical conduit to the pond. The downside is that I have to dig up the
patio stones again, although I may tunnel (water drill) this time.

One problem I see is that the top of the barrels would be below the level of
the pond, unless I raised the barrels. Raising the barrels is probably safer
from a leak perspective, but it would mean having 500 ponds 4' off the
ground. A couple of other pros I can think of are having the aerator/heater
inside during the winter.

Any one else done this? Any cautions/ideas?