What's the best way to put invisible for user but indexable link?

Question

I have several sites on the same topic but still competitive to each other. I would like to put cross links on these sites in text so they won't be visible/"clicakble" but still indexable by search engine. What's the best way to do it i.e. what kind of HTML/CSS magic to apply?

As far as I understand this is a "White Hat SEO" technique and will help to increase relevance of the web sites.

Answer 1

I would advise against doing it. Search engines get better and better at detecting such tricks. No matter what you do, some day search engines will notice it. It's not worth it and it's certainly not "white hat".

From http://www.google.com/support/webmasters/bin/answer.py?answer=35769 (emphasis mine):

• Make pages primarily for users, not for search engines. Don't deceive your users or present different content to search engines than you display to users, which is commonly referred to as "cloaking."

• Avoid tricks intended to improve search engine rankings. A good rule of thumb is whether you'd feel comfortable explaining what you've done to a website that competes with you. Another useful test is to ask, "Does this help my users? Would I do this if search engines didn't exist?