I did this to have an excuse to do an automation project.
A downloadable tool for Windows
This is a tool for Garry's Mod that downloads and wraps Valve's SteamCMD then uses it to resolve checkerboarding and errors using the server version of Counter Strike Source.
All you need is the directory where gmod lives.
Ex: C:\Program Files\Steam\steamapps\common\GarrysMod