Select a tray. You can use a boot or shoe tray designed to hold footwear, or any serving tray or pan with a rim around the edges.
Cut a piece of shelf liner to fit the bottom of the tray. This is not required, but will make the tray easier to clean.
Add river rocks or large, smooth pebbles to the tray. Place them flat sides down and use enough rocks to fill the tray to the rim. River rocks can be found at most garden stores.
Place boots or shoes on top of the rocks. Mud and water from the shoes will drain through the rocks.
Remove the rocks regularly to clean the tray. If the tray has a piece of shelf liner on the bottom, lift the shelf liner out carefully, shake dirt and debris into a trash can, and rinse or sponge down the shelf liner. If the tray is unlined, rinse the tray to remove dirt and debris.