Go to the Likes page on your timeline. Click the Edit button in the upper right. Privacy visibility buttons will pop up next to each Like category for you to change the visibility of Likes. Make sure to scroll down to the bottom so you don't miss the last category "Other Pages You Like."
Yes, Facebook intentionally doesn't do a good job of advertising this. For me, though, I'm satisfied that the option is there (and that my option to stalk my friends is there as well).
I have a direct link to privacy settings in the header. I don't know how can they make it more visible.
I dare you.
And if he manages to do that, ask him to chart one which will be valid 2 months from now.
They keep changing that shit. Keeping up to speed is just a completely overwhelming sort of task which even most people who care about privacy wont have the stamina to do.
Even if the privacy settings do allow you to opt out of being visible in Graph Search (and there is an open question of if it would for a query that returns other people instead of you), now people's safety is involved for something they themselves have no control over.