hidden content without penalty

Hi I have 2 websites of my clients, I need to put a link inside them in to my main site, one site is built from word press and other one is custom html site, the thing is customer don’t want to see my link on his websites, and he have admin access too, but he haven’t clear idea of cording. So...

Hi Everyone Please advice me more about Hidden text, as my client requires few content in is page that too he have given now I have to enter few more content in that like hidden text. Please guide me on this. hidden text without penalty