how does george know were to fing lennie in chapter 6?

George kows where to find Lennie because he had directed Lennie to the brush as a safe place to meet at the beginning of the novel.

'Lennie - if you jus' happen to get in trouble like you always done before, I want you to come right here an' hide in the brush.'

Sadly, George is used to Lennie getting in to trouble: they had been run out of the last town they were working in because Lennie had touched a girl's dress. He has to set up their escape plan before they even reach tehir next job.