I've seen the opposite of this -- have a link on the site footer that's unlikely to be clicked by a user or prefetched, but as soon as a robot GETs it, the rest

I've seen the opposite of this -- have a link on the site footer that's unlikely to be clicked by a user or prefetched, but as soon as a robot GETs it, the rest of the site is replaced by syntactically valid gibberish.