I went to the Container Store and purchased a tray that's used for wet shoes/boots. It too has an edge so any wee wee that runs off the pad will remain in the tray and can be washed off with soap and water. The only problem is that the tray is not wide enough for the entire pad so I usually have to "flip" it to get to the other 1/2.
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Romeo  and Sujata 
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