There's another alternative to the litter box for keeping the pee pad in something and that is a potty pad holder. We bought ours online. There are a couple of different styles. Ours has a plastic floor and a frame that snap down over the edges of the pad securing it to the floor of the holder. We bought the one we have because our baby is used to the larger pee pads already.
Here is a link to what we have:
http://www.workingdogsweb.com/store/...ds_FT_650.html