Thanks to all who replied. I don't have a way to set up a night camera. I've
been suspecting a heron but haven't seen any which doesn't mean it isn't
around. After a thought I did some checkin and we have Black crowned Night
Herons here whiuch are nocturnal, so that maybe the reason i don't see it
during the day. I am gonna try the fishing line across the pond. I did build a
large hiding area for them to get under which is made of large 3ft x 2ft
stepping stones,they seem to stay under it now. Thanks all.

Scott in Louisiana