I can't access the page at the moment:
HTML::Template->new() : Cannot open included file text-link-ads.html : file not found. at Modules/HTML/Template.pm line 666.
For help, please send mail to the webmaster (root@localhost), giving this error message and the time and date of the error.
If you are adding a border-bottom on hover then that will cause a shift in the layout. You don't really want to affect the flow at all when hovering as browsers are not required to reflow the document although most do.
Depending on your situation you could perhaps add a border by default in the current background color (or transparent if ie6 support isn't needed) and then just change the border-color on hover and not create a reflow.