If you are using a mallot with one smooth side and one jagged, such as this one from OXO:
You can use the smooth side which will make less of a mess. You can also use the side with ridges, but try adding a sheet of wax paper over the meat and pound through it. It not only keeps the meat under cover but it doesn’t get the hammer as dirty. You’ll still want to clean it and everything else with hot soapy water when you are finished, but hopefully you won’t have to clean a messy counter too!