"There will be surprises this week, no doubt. This is the end - the final whistle. There is no coming back and teams won't want to be conservative and wonder 'what if'," said Deans.
"It hasn't been straightforward. This sereis has been demanding on and off the field in every way. If we are able to work ourselves into a winning position it will warrant a little bit of satisfaction and reflection.
"But we've got it all to do and we understand that. We have a lot of respect for the Lions. We've seen so far how hard it is - they don't give you anything.
"We are going to have to earn it in every way, but we wouldn't want it any other way. I thought I had my toughest week last year, but it has since been superceded.
"It's a great week in rugby. Brisbane had the experience of the Lions, then Melbourne and it has been a great series. The culmination of this series is going to be huge and it is Sydney's opportunity to get involved."
Deans was delighted to hear the news that his captain, James Horwill, had his not-guilty verdict over his citing in the first Test upheld overnight after the challenge to the original decision by the IRB and has received a second boost in the return to full fitness of the 110 times capped flanker George Smith.
Smith was added to the Wallaby squad ahead of the second Test after recovering from injury, but not considered for the game in Melbourne. That could all change in Sydney this weekend and Smith, who celebrated his 21st birthday by helping the Wallabies to beat the Lions in the decisive third Test at the same Sydney Stadium as Saturday's game will be played, could make a dramatic comeback nearly four years after his last Test.
"George has a week of training under his belt, so he has some background with us and, yes, he is physically fit enough to be able to be considered. It is good to have him in the group and even last week he offered us good value," admitted Deans.
"As happens, the Lions responded well last week and really targeted the wider breakdowns and they put us under a lot of pressure. We have got to be better."
Lions skipper Sam Warburton proved to be the master of the breakdown at the Etihad Stadium last weekend, but the hamstring injury he picked up in the second half has ruled him out of the third Test. Not that Deans believes that will give his side an edge.
"They have got some quality options there and it won't matter who they choose. They have some very good and able replacements," said Deans.
"In fact I think it was you blokes (British & Irish media) who were suggesting that they should have been there in the first place. Such is the choice that Warren has. I won't spend any time thinking about his selection until he announces his team."