"He's a fantastic asset to us and I wouldn't like to put a time limit on him. He's in fantastic condition and so fit that he could play on well into his forties I would imagine.
"So many other people look at him as the best English goalkeeper now and I don't think there is a better one around. I wouldn't swap him for any other, to be honest with you.
"When I took him from Manchester City I spoke to (former boss) Stuart Pearce and Steve Wigley up there and they said he had been absolutely fantastic for them that year and they could only remember him failing to save one goal that he should have saved.
"They said they couldn't tell me just how many goals he saved which he had no right to save but that's how he's been with us. The amount of points he's saved us over the last two years is unbelievable.
"He used to have a problem, I think, before with his concentration, not his goalkeeping - he would almost get bored at times and want to get into the action.
"But I think he's learned to concentrate more and knows he now has two centre-halves in front of him who can head the ball. He's learned when to come for it and when not to come."