There are currently some high traffic posts/threads on my forum. But they usually also contain some sort of outbound link. This off course doesn't really give a visitor the opportunity of clicking my ads or joining my forum. I sort of want him to end at the end of a street and see him thinking wether to enter the pub.
So what i'm thinking about doing is setting the bbcode to only display links to registered members and for unregistered display a message like links are only available to registered members.
Still that may be a bit annoying to new people to the site.. dunno
You could, if you are comfortable with coding, hack your board so that the link displays as plaintext to guests and a clickable link to users... Then if the guests want to visit they have the hassle of copying/pasting the link - that should keep them around a little longer.
However, if the post is specifically about whatever content is on the other site then you have to expect that people are going to want to go there!