Mine also prefer grass or dirt. As it is, it takes Bella quite some sniffing time to find just the right place to squat. Ripley of course looks for the nearest tree. The only time they have ever gone anywhere else was when there was a lot of snow and we hadn't yet cleaned off the deck. They both pottied on the deck but really had no way to get down into the yard. Ripley used the area under the deck (it is dirt and stones under there) when we had almost a blizzard a few years ago rather than journey out into the yard on the little path we had shoveled for them.