I have a field where the client can enter a URL, and then that field's value is put into the 'href' of a link in the template. The client will sometimes prepend it with "http://", sometimes with "www.", and sometimes with nothing. Unless it's prepended with "http://" or "https://", the link is interpreted as relative and tries to go to "http://mysite.com/www.otherlink.com", which is obviously not what I want.
What's the best way of automatically handling different URL formats?