"Pia" wrote in message
...

I can't really put mesh below the surface of the water, as the fish eat
food
which is on the surface. I had considered putting a mesh over the top of
the pond itself (as the "walls" around the pond go quite a bit over the
water level). This is likely to be our solution if we decide to keep the
pond.

I was thinking of a fairly large mesh - 8swg x 2" (4mm wire at 52mm centres)
is fairly readily available as it is used in some security and safety
applications. That size does not cause problems for quite large goldfish.
However, if you think there would be a problem with the Koi, you could
always have a dedicated feeding spot, which has a lockable section of mesh
that can be removed to feed the fish. As there will be someone there to feed
the fish, the hole will be supervised and should present no danger to a
child. Above the surface will work as well, but is rather less attractive.

Colin Bignell