Body bleeds into sidebar

Hello,

In order to float my footer away from my sidebar (footer not touching the bottom of my sidebar) I used the following code:

#secondary {
margin-top: 15px;
margin-bottom: 15px;
}

#colophon {
margin-top: 15px;
margin-bottom: 15px;

It worked great, but, when I tried the same thing from #primary to #secondary to get a space between my body and sidebar when the browser window is tightened, it did not work. So, when you narrow the browser window, my sidebar falls below the body and backs right up to the bottom of it. Is there a way to correct this and leave a small space between where the background image show through?

Thanks,
Jenn