trying to get underline on nav bar, twenty eleven

Hello all I am trying to get it so that whatever the current page is, there is an underline on the nav bar. For example you ahve jsut clicked on the about page it loads and about has an underline on the nav bar but none of the others do.

I have tried adding text-decoration: underline; #access hover, but it doesnt seem to do anything, any body got any ideas?

here is my site: http://osbornerestoration.co.uk/

thanks in advance

Harry