Silo is a fad-trend from a long time ago back in the days when keywords mattered more. It took the idea of site architecture and over-simplified it. It reminds me about that joke about SEOs:
An SEO goes to a bar, a tavern, a public house, a gin joint, a pub, a dive, a bar and grill, a bar and grille, a grill and bar, a place to drink.
Good site architecture is about starting out with a general concept at the home page then gradually becoming more specific as you click through the pages, drill down as they say. This is a pyramid type structure. An example would be Webmaster Forums > Marketing > Link Development. Once inside the Link Development section it's the wide variety of link building topics.
Focusing on keyword anchor text within ones own site is ten years behind the times.
One, the effect of your own on-page SEO has been dampened. It's a less-trustworthy signal.
Two, it's not about random keywords seeded at the footer.
Three, footer data is dampened, i.e. thought of as less important. Four, the entire page is examined for meaning.
Five, the pages and site are profiled to see if they are within the realms of normal (panda/penguin etcetera) or show evidence of trying to influence the search engines.
What you're up against goes on an on. Seeding pet keywords at the footer of your pages, in my opinion, is futile and possibly counterproductive. Just do what makes sense for your users.
