I find them in the oddest places
And why is it they seem to like doing it just after you have cleaned the trays and swept up all the bits?
Turtle Mat actually make one that says "Please wipe your paws"
http://www.turtlemat.co.uk/Pet-mats-dog-mats/This has given me an idea. I might try a turtle mat in front of a tray and see if it helps.
If so, there is a cheaper but still 100% cotton version called dirt trapper and I will get those. It won't work for Alice as she always sprints front the tray
(The same cat that hobbles around like an old lady
)