Each time a cat uses his litter box, there's a chance some litter will get onto the floor. Worse, some cats miss the box entirely and go on the floor. A spill tray underneath the litter box is an ideal solution and can easily be made in a short time.
Making a Tray to Catch Litter Box Spills
Place the litter box into the plastic container. There should be at least 2 inches of extra room on each side when the box is centered. After ensuring it will fit, trim the sides of the container so its top is about an inch off the floor. Use sandpaper to smooth the edges in order to prevent injury to your cat's paws.
Flip the litter box over so the open end faces down. Use glue or epoxy on the corners and in the center of the box, center the container over it and press the container face down on top of it. Use the weight to hold it in place and leave it to dry as per the instructions on the adhesive.
Ensure the pieces are bonded together by pulling gently on the edges of the box and tray. More adhesive may be necessary, especially for larger boxes.
Depending on the eventual location of the litter box, this step can be completed in two ways.
If the box will be on a solid, flat surface, a piece of rubber sheeting can be taped to the floor and the box with tray can sit on top of it. This will prevent sliding and also offer another form of protection from stray litter pieces. If it still slides, rubber washers or stoppers can be attached to the bottom corners of the tray.
For a carpeted surface, Velcro can be used to keep the litter box and tray in place. The hooked side of the Velcro should be used, as it will latch onto the carpet without ruining it. An adhesive Velcro can be used, or the same epoxy used earlier will work, too. Attached this to the corners of the bottom of the tray, and simply press it down onto the carpet.