I have a quite shallow pond (18" or so) in north London, u.k. . I built a
substantial little house out of bricks for the gold fish to hide under. It's
complete with a ventilator type grill on the roof. (the kind you put in the
wall of your house just above ground level to assist air flow around the
foundations) The purpose of this was to enable the fish to see out from
their house.

The other day a heron flew in (we chased him off several times) and he ate
them all, when we weren't looking.

Somehow I've never liked nets over the pond, and would prefer to build a
good house for the fish; preferably so they can see danger coming. I
beginning to think maybe some fine mesh type chicken wire, so they can get a
good look around, but be safe under it?

Would anyone have any ideas on how to design something suitable please? Or
are the fish just too dozy and inattentive and really the whole pond has to
be covered ? Thanks for any advice.