I haven't really targeted bulls a lot with the fly rod, but here's what's worked for me when they lie on the bottom
& won't take anything you put in front of them: tie a heavy marabou or rabbit strip jig on the spincast, let it sit on
bottom a foot in front of the trout's nose for 30 seconds, then give it a twitch. More often than not, that bull slams
that jig like he just caught it in the redd with his wife- no subtle take, just extreme trout-on-jig violence!
I'll go out on a limb here & guess that this method would be a lot harder to duplicate with a flyrod ( too much drag
from the current), but in some cases it should be doable. Maybe we should all carry the "Popeil Pocket Fisherman"
with us for these situations?