One thing you can do is to link out from popular pages (popular with the SE's) to such an extent that they no longer rank. Something else that makes some sense is to look at pages that rank for stuff that's not relevant for your website: rephrase the title-tags and do some on-page optimization so that traffic coming there becomes more relevant (and perhaps less).

I think the title of article can be more accurate by rephrasing it to read: How to get Alternative Sources of Traffic Other Than Search Engines.

I understand the notion of not putting all your eggs into one basket but even entertaining the idea of disallowing search spiders is most certainly not the way to go.

What are the other sources – in the most general view?

Marketing Strategy:
Radio, Local/National
New paper, Local/National
Direct Mail, Indirect mail marketing
Advertising on relevant sites – Affiliate Marketing

On-Site SEO:
Use sticky content – News for your industry – to get visitors returning regularly.
Email a friend feature
Provide RSS Feeds feature
A Blog is a must have
Emabed/Link to this page feature
Newsletter subscription

I have to admit to link baiting when I wrote the title. Guess it worked :-)

Yes, my objective is finding other sources, thus reducing "the percentage of search traffic" while not actually reducing the amount of it.

Right now, I'm working on doing a t-shirt/cash give-away as a way to get some new content. I've been too busy to write lately. We'll see how it goes.