* There is no point in using excerpts, if you dont plan on showing more.
you better just show the full post and forget about using an excerpt
an excerpt is an excerpt .. and nothing else ...
* if you want a link back to "where the visitor came from"
you need to either catch the HTTP referer field, as soon as someone enters your site, with some custom coding
and store it in a cookie or so, to make sure its not lost while the user might be clicking other links on your site
then use some custom coding to retrieve the referer from the cookie when the users clicks some "go back" link
but i think that is beyond the scope of this forum
you could put a "go back" link in the footer under a post
ata > Edit Post/PAge Info Items > FOOTER: Single Post Pages
and add this:
that would just send the visitor back to the previous page in his/her browser
same as manually hitting the "back button" in ones browser