Apparently I am lucky because I don't have any cats and there aren't any in my neighborhood (just lots of dogs), so I am able to have this super awesome backyard sand pit for the kids to play with and not have to worry about cats using it for a litter box.
I made this last year early in the summer and it has held up very well. I did add several more bags of play sand a month or so ago to fill it out a but more, but overall it is a fun sandy area for the kids to scoop, dig, and build in. Just notice all the random scoops that have wound up out there.
Anyway, to make the sand box, I first enclosed the area with chop stone on one side (luckily the other sides are bound in by the fence and patio concrete). Then I covered the ground with landscape fabric so no weeds would pop up. I then cut a small hole in the center and pushed the umbrella in deep so it wouldn't fall over. Last came the sand. I can't remember how many bags I got, but the sand is about 6-8" deep. Now all that was left was to add some cute adirondack chairs and some sand shovels and buckets and let the kids loose.
Overall I think it is a great addition to the backyard and a fun activity for Madeline.