[pokernicus]

I think you played this perfectly on the river.

The fact that he fired twice makes it likely he has an Ace. And he can easily interpret your calling as saying that you have an Ace or a Queen. When the case Queen falls on fifth street, he probably thinks you are more likely to have an Ace (since Quads are the last thing people suspect). Also, if he is holding an Ace and there is one on the board, he is less likely to think that you have pocket Aces (giving you Aces full).

It's hard for him to lay down the third best possible hand when the top two are pretty unlikely. And no one likes to be bluffed out of a chopped pot, so even if there's a remote chance you're bluffing, he's probably psychologically inclined to call.

The only thing is that whenever someone does the check/call flop, check/call turn, push river, 95% of the time they have a monster hand. Still, it's hard for him to laydown any hand with an Ace.