One of my go to moves on ponds with stockers was to cast out a bushy mosquito pattern and tug on the line just enough to pull it under and then let it rise back up. They would take it just below the surface. Only works a couple times before you have to false cast like a lunatic to dry it off again.
example:
https://www.orvis.com/mosquito-dry-fly/0331.html
I haven't been fishing like that in a while and when I tried last season I kept watching rises and trying to get in front of the fish like I was casting at bones in the salt flats. That doesn't work, they are more unpredictable with direction of travel and you will spook them.