if you have a good relationship with the site owner, then write an article and give yourself a contextual backlink and have him post it on his site. and just provide an internal link from one of his inner pages. readers do not need to know about this page, just google. you will get more benefit this way than site wide / footer link.
take a look at this:
https://neilpatel.com/blog/links-building-google/
many want to bash neil, but what he provided in that research is directionaly correct and you cannot argue with the results that he found.