If you don't want the players to know the cliché weakness so badly, why don't you make up another monster instead of troll? Just sidestep the whole problem. It's not Troll Canyon. It's Grall Canyon. What the fuck are Gralls? No idea but they sound nasty.

Because clearly, some players are going to balk at "you want us to forget this well known fantasy cliché?". And it doesn't matter if you think their playstyle is stupid. It's a game. People are trying to have fun.