Wallabies coach Michael Cheika is keeping his players on their toes by employing the unusual tactic of picking two completely different starting sides for the first two matches of the tournament.

It's that sort of unpredictability in the way the Wallabies play that assistant coach Larkham hopes will give them an edge and players are fighting for game time.

Larkham, who was part of Australia's 1999 World Cup-winning team, said the Wallabies are still trying to find the right balance between out-and-out attack and a strategic mentality.

"Guys have roles to fulfil within the team … for the leaders it's about making sure they have an understanding of what decisions have to make at certain points of the game," Larkham said.

"The game has changed quite considerably [since Larkham retired], in 1999 we were the best in the world defensively and we were cutting edge.

"Most of the teams have caught up now, there's not a lot of give and take. There's different tactics, bigger players … there's less give in the games now. We want to seem unpredictable at times."

Soggy conditions greeted the Wallabies as they continued to ramp up their preparations in Bath.

Having just three days between their first two games will give Cheika the chance to experiment with different combinations and ensure all players get match time.

"You've got to spend time with all your possible combinations because you have to learn different timings and what guys want," said winger Rob Horne.

"You're always interchanging and learning … we want to be prepared for everything.

"This is the most competitive team I've been a part of. I haven't played 100 Tests, but in my short time with the Wallabies it's the most competitive it has been. That can only bode well."

The halves selection will be the most contentious with Quade Cooper, Bernard Foley, Nick Phipps and Will Genia jostling for spots.

Genia has been eased back into action after a knee injury, but Larkham declared the former Wallabies captain had rediscovered his best form.

"Will's very motivated at the moment, but we don't want anyone to overplay their hand," Larkham said.

"His defence is good, when he's at his best his defence is really good. Everything falls away when he's not at his best, but we've seen this year he's back where he needs to be.

"There is confidence in the back line, but it's not just about the attack. It's about the getting the balance right."