shelves are another concern with livestock as if the pond is 30" deep your shelves will probably be at 12" or 18" so even though the fish will run down to the 30" deep section the predator will just stand on the shelving. Im usually very against any type of shelving in a pond containing any type of livestock. I have done things where I would build a separate bog on the outside parameter. I mean really ill do whatever the customer wants but those are my recommendations and my insite for the future. What i notice is people always tend to turn a water garden into a fish pond, then they hear about and see koi and then add koi. Which as im sure you know if a customer says oh no its just a water garden no fish youre not going to design the pond for fish, but then it happens later on so I just spend a lot of time with the customer and let them know what they will need
As for decorative ponds that is mostly all of my business, not really many people want to keep a strictly koi pond. I admit they are not all that appealing to the eye if you like the natural setting, sure it can be done but a real koi pond doesnt consist of plants, shelves nothing other then fish and lots of people dont like that. building koi ponds is my passion and if I could that would be all i would build, but its just not the market too many people are afraid of keeping fish or all too often have had a bad experience of putting fish into a pond designed for plants.
There is a lot of good predator protection. have you heard of the Scarecrow? I know a lot of people have luck with those