When I was told I was allowed to get a little dog, one of the conditions was that I toilet train her as she was going to be an inside dog.
I did a lot of research into puppy mats and came up with Conni Critter Mats http://www.conni.com.au/shop/Conni+Critters+Pet+Pads+-+washable+waterproof+absorbent.html, she uses them all the time. When we are on the boat, at home if it is raining and if we go out of an evening and she is left at home.
They are fantastic, we pick it up and chuck it in the washing machine.
This mat is one that we use on the boat because I have sewn corners onto it so that we can put lead sinkers (weights) in the corners to hold the mat down so that it doesn’t fly away in the breeze.
We always keep a clean mat on the floor so she can go whenever she wants. They are a lot cheaper than having a doggy door installed and we can take them on the boat.