i agree that firing a 3rd barrel here won't work, and a lot of time FISH see shoves as weaker than some sort of 2/3 or 3/4 pot value bet...
these guys just DONT fold top pair, period. which is great for when I hit my river, in fact this also means that if the river comes an A i have to value bet it, i would think around half pot would easily get called.
i did also realize that they will check this back on the river many times and if he was on a draw I will win as well which is great.