"Maybe over the past couple of years we've played nice, pretty football but lacked that bit of toughness."
But he said: "There's been times this season when we've toughed out results - Smithy and Heinze will run through brick walls and set an example for everybody.
"Smithy's come from Leeds, one of our biggest rivals, but he's immersed himself in the club and set a tremendous example from day one.
"From the first day of pre-season, he's integrated superbly and on the field he's probably been one of our most consistent players.
"He is a player that never moans, he'll play in any position, and he's just the type of player that we've needed.
"Gabriel is probably one of the toughest players I have ever played with. People go on about Argentinean defenders being tough and I've seen that at first hand. His aggression and the way he defends has rubbed off on the rest of the team.
"Smithy and Heinze have brought a toughness to the team."