1st off, don’t use tables for layout. Your menu is not tabular data , so style it with CSS. 
2nd. DONT use: position:absolute on your main design. It takes things thing out of the regular flow,
3rd Use a container (you are actually already doing this, but I am mentioning it for good measure.
if you follow these 3 rules your container height ( see #3) will always be the sum of the height of all it’s children (in other words divs will appear to go to the end of the container)