That's honestly a toughie, maybe you should actually wash their
paws throughly when they are ready to enter the house. Otherwise,
I would just say keep them off the furniture and bed, tiled floors you can always mop.
Oh, or you could also purchase some of those little dog booties
for them to wear on their feet...now there is an idea!! :P
http://www.yuccadune.com/media/PawPalsDogBooties.jpg