Build a wood frame that will fit the top of the box, then put screen wire on it, Will be easy to take on and pull off when the kids want to play, the screen will keep the cats out of the sand.

Make a cover for the box and use it. Only way to stop the cats. If you see a stray cat in your yard, spray it with water. They might get the message and not come back. Good luck.

We used a square (the size of the sand box) of plywood with a 2x4 frame. Put hinges on one side and a latch hook (like on a wooden screen door) on the other. When the kids wanted to play we simply unhooked it and flipped the lid open. When not in use, hooked it closed. This also helped to keep the racoons out too. ;-)

I also agree with using a tarp.

I agree,just get a tarp.

Suggestion for screening to use, it is called pet screening and is sold at the big home store. As quilters we use it for making purses.

we took wire fencing that comes in small rolls about four feet high and put that around the dirt for planting (we plant in kiddie pools.less weeds and is like container planting.)that keeps the cats, squireels and possums out. when we need to get in just take off the twistie and pull back rolls right back up and set it back when done a twist top and bottom with twistie or tie.

Cats don't like chicken wire either, (or tin foil to keep indoor cats out of potted plants!). Maybe you could fashion a lid out of the chicken wire.

I use heavy tarp type material from the home store and I use those black binder clips to attach to the frame.

We had the same problem...the neighbor's cat..UGH! The neighbor just smiled and explained that he was an outside cat. So we covered it with a tarp like cjomamma advised and used logs from the woodpile to keep the tarp from blowing. It was a pain to uncover. Kids could not do it by themselves, so I always had to help. And definitely had to remember to cover it back up.