[SOLVED] Page menu drop-down content appears underneath widget content

Hi all, I'm having a bit of trouble with the Page menu bar - the drop-downs for sub-pages appear underneath the content of one of widgets in the LH sidebar. Screen shot attached. Site is http://marinecentre.co.nz/ although you won't be able to see the issue there at present because I've implemented a temporary fix by increasing the padding between menu items so the drop-down doesn't conflict with the widget. Would prefer to find a permanent fix however, if possible. Cheers!