Place a banner ad outside of the main container

[Craig Tuller]

That would not be a very good idea since the theme is setup for most monitor sizes. If you place something in the gutters, on some monitors and if someone increases their screen size using a ctrl +, your vert. banner will not display.

That is why most sites have sidebars, so that ads can be displayed on all pages. Sidebars typically are coded on the right, also for a reason, several actually. One, reading left to right, visitor sees the important stuff first (& no ads are not important to the visitor), and another reason is what the search engine spiders see first in the code, the important content.