There was an error in the code you offered.
<?php echo(isset($_GET["accesscheck"])?$_GET["accesscheck"]:"defaultpage.php"); ?>
when I tried to update the behavior. It kept coming back blank. I had to add the get value "accesscheck" to the bindings tab, use that, and manually edit it. Then I realized there is a parenthesis error. Should be:
<?php echo (($_GET['accesscheck'])?$_GET['accesscheck']:"defaultpage.php"); ?>
<?php echo ((isset($_GET['accesscheck']))?$_GET['accesscheck']:"defaultpage.php"); ?>
BUT it would not accept the second version.
It would be nice, under this methodology, if WA used something more generic than accesscheck like redirect. I want to use the behavior for more purposes than just an inappropriate page access such as when someone clicks on the login link from any page on the site, OR they try to access a page that requires login. The easiest way for me to do this is to make those links include the url value of accesscheck, but that does not really describe what I am using it for.