Can ads be responsive?

I've installed ad sharing.
I have chosen the leaderboard size and it looks fine at my site
but at my members site (witch has an other theme) the ad size is to big, so it is overlapping the menu.
Is there any way to auto-resize the ads? Or do I have to choose an other size for my ads?

I see the same problem when viewing the site from my mobil. The ad does not scale own to fit the responsive theme on the mobile.

Thank you in advance
Mette