If you've got graffiti covering a section of the walls around your yard, sandblasting is the best way to remove the paint. Before the sandblasting, you should prepare so that you, your family, and your property all remain in good shape and don't get blasted along with the paint. While the sandblasting company should provide help with cleaning up, you're going to have to plan carefully.
Corral Your Pets
If you have pets that usually stay outdoors, corral them indoors or take them to a pet daycare for the time being. While the pets should be smart enough to avoid running toward the sand, you don't want them getting freaked out by the noise and possibly trying to escape your yard. If they do get out, there's no guarantee they'll come back. So, get them inside or move them off the property entirely.
Plan on Blasting a Whole Section, if Not the Whole Thing
Even if the graffiti covers only a small part of the wall, you should still plan to have the entire section blasted. The sand will take off all paint and dirt, meaning that the wall could end up looking like it has a pale blotch in the middle of it if you don't have the entire wall done. You may as well blast the whole thing and give it a good cleaning while you're at it. Then, the wall will be the same color all around once the blasting is done.
Plant and Soil Cleanup
Before the blasting, put a tarp over plants and soil so that the sand doesn't wind up settling in and affecting your ability to plant anything. The sandblasting is a high-velocity task. While the tech wielding the sandblasting wand might look like he's moving slowly, the sand itself is coming out at top speed. It's going to ricochet off the wall and onto plants and the ground nearby. Once the blasting is done, you can remove the tarp along with the sand and paint residue.
If there are trees in front of the wall, and you want the wall by those trees to be blasted, too, talk to the blasting company about how to protect the trunk. The company may have tarps they can wrap around the trunk to prevent ricocheting sand from lodging in the bark.
Once the blasting is done, the wall will look nice and clean, the plants and soil around it should be safe, and your pets should be able to return to the yard and run around again.
For more information, talk to companies like Dustless Restoration.