1.) Don't let him grab your legs. It's a worst case scenario if he even just one of them.
2.) Fracture one of his arms. You will deprive his ability to use his shoulders if you do so.
3.) Make use of your: Wrists, elbows, chest, arms, hips, and most of all your ankles because extending your ankles is always the easiest way to prevent a shovel; except when you're already in the air.
4.) Refrain from EVER JUMPING. Shovels are at their best when you do so.
5.) Some players who use shovels might just be novices and still don't know much about Toribash. Applying #3 will most likely to prevent a shovel from any novice. Monster shovellers are the smartest shovellers and might even have to make you use all your joints, so be careful about them. Again, apply #3 and do the rest for yourself.
6.) Shovellers just push you into the air and pull you down outside the dojo. It won't really work if you use the last resort: Ankles. Use your hips, knees, and ankles for extending and raise shoulders to revert his momentum and use it as your own and make a comeback.
7.) Grab his legs. Shovels won't work at all when you do so. Even if they do, it'll carry the shoveller itself too.