stop search including permalinks

How do I stop the search function using permalinks to generate results? I have that option disabled but when a portion of the permalink is entered in search, the results include posts with that permalink – which is *all* of them.

I want search to respond to title and content only. If the permalink is entered (and its different to title and content) I’d rather have zero results (as opposed to every single post, which is what I’m getting at the moment).

What am I doing wrong?

Thanks for your time