That is my message to the Wales team as they prepare to face their massive World Cup pool match against Australia tomorrow.
The Wallabies fly-half is 33 now, with more than 100 caps, and he is truly a world great.
He is such a creative player, and it is very difficult for any team to stop Australia from scoring tries when they possess individuals with such creative skills as Larkham, Stirling Mortlock and Chris Latham.
Wales have to target Larkham, it is as simple as that. He is probably the key man to this whole mouthwatering Millennium Stadium contest.
Wales need to get as many of their big guys as possible running down Larkham's channel. If they can do that repeatedly, then by the time he gets the ball he will be tired.
They need to rough him up a little bit - not illegally - and get him into a few rucks. If Wales do that, it will be a sign of massive respect for him.
Make no mistake, home advantage will be huge, especially in a game of this magnitude, but Wales have got to control the situation and thrive on it.
Australia have been moaning a bit about having to play this game in Cardiff, but that is just the way it has panned out.
I hope everyone in Wales - those in the stadium and those watching at home - really get behind the boys. This is going to be one hell of a game.
I was very impressed with Australia's performance against Japan last weekend.
Yes, they took 20 minutes to score a try, but tactically they delivered a superb display. They didn't deviate from their plan - they had runners out wide and they kicked a lot to their wings.
They were also devastating in the loose. George Smith looked back to his best - I think he is relishing the challenge of keeping out Phil Waugh - and Rocky Elsom is running some great angles.
If Wales keep playing a pick-and-drive game, then they are not going to get any change out of the Wallabies. What Wales need to do is play like they did during the last 20 minutes against Canada, and then they have a chance.
Rugby is so gain-line orientated these days, but against Canada in the first half no-one carried the ball and their pick and drive game just didn't work.
When Stephen Jones went on from the bench he changed the point of attack. If they do that, and the forwards put their hands up, it is a game Wales can win.
Make no mistake, Wales have got to play well to beat them. They will have have to play like they did when they beat them in November, 2005.
Slowly but surely, the Australians look to be peaking at the right time. Don't forget, they've beaten New Zealand twice in the last year.
I think for Gareth Jenkins to start with Stephen Jones at number 10 is the right call. I am not taking anything away from James Hook, but Stephen is more direct and has more experience.
He hasn't the skills James has got, but James hasn't got the experience Stephen has got. Stephen kind of orchestrates the side.
I think there will be a huge role for James at this World Cup, and Gareth Jenkins might have been tempted to go with him at number 12.
But because of a lack of penetration in terms of getting over the gain-line, he probably felt he would have to go with the big centres in Sonny Parker and Tom Shanklin.
As for the other games this weekend, I think I will stick my neck out and take the All Blacks to beat Portugal, but Ireland will need to find some form and tempo against Georgia, who looked good against Argentina with their strong pack.
And then these is Samoa versus Tonga on Sunday afternoon, which should make for some lovely family viewing!