Well they not my fish, mum and dad went to Egypt yesterday, and I got to look after my dads fish

(they are his pride and joy!!!).
Got up this morning opened the back door curtains and the fook off HUGE heron flew off

......so now im panicing, we have wire running around the pond, which is "supposed" to stop them getting at the fish, but Im not soo sure.
Ive put a load of big plant pots around the edges of the pond pmsl

but is there anything I can do, bar sit and wait for them all to disappear, and please dont sugest killing it, that would be impossible unless you shot it, which I cant

dont have a sodding gun!!!!
any help would be sooo apprecaited, something ALWAYS goes wrong when my mum and dad go away, just hoping that this isnt going to be the thing that goes wrong