Is it possible for me to check whether or not my landing page URL has been visited by a visitor on my site? (and in the case that it has not been visited, serve a redirect to it?)
My problem is, that I need new visitors to view my landing page as the first thing they see. This (of course) does not happen when a visitor copy/pastes a link from one of my sub-sites to someone else.
I have been searching for a bit, but have come up empty handed. Is something like this even possible?
Yes you can check if a visitor (IP or COOKIES or Session id) has been visited your landing page! This is possible with a few PHP lines of code. But the best SEO practices recommend do not force redirect a visitor on a page. You can propose to the visitor a CALL TO ACTION link or banner linked to your landing page.