the first million of insurance is the most expensive...additional layers over that are less so IMO the more the better. Signs, in and of themselves probably dont mean much, a sign cannot transfer liability...its all about liability and unfortunately or ironically if there was some sort of negligence then there is liability the insurance carrier becomes "you" and will settle anything involving an injury or worse.
that said yes a good no tresspassing sign is the right way to do it but probably additional wording wouldnt be required. Somehow it seems pointing out that there is a pond with a sign might be construed as negligence as a body of water is an attraction to youngsters. The less they know the better off you might be.
All just my opinion.
I know around here the insurance companies are nervous about ponds and swimming pools are required to be fenced in...maybe ponds are next.
