Like others have mentioned, I also have stopped using a footprint for my tent. I find the thin mesh parts break-down before the floor.

I have heard of people using painters drop-cloths, but they don't hold up very well. Tyvek (home insulation cover) and polycryo (window insulation film) are more popular options I have heard of; also available at home depot. I think a few online cottage gear companies sell small sheets of the stuff for this purpose.