Just for what it's worth, I am very carefull where I place landscaping rocks! Large rocks don't go well with tractors, ATVs, snow removel and just about anything else that moves. I place rocks only in inaccessable areas or between clusters of trees.
We had one such large rock out in the open years ago. I didn't even have a drivers license back then. Anyway, I was teaching a GF how to drive the tractor. Long story short, she hit this stone, throwing us both off. But as she was thrown back, she pulled back on the throttle lever, the tractor front wheels came back down and the tractor proceeded to drive into the house. My father was not impressed! This woman probably has pain in her tail bone to this day from her hard landing.
Two things I learned from this. One is about placement of such obstacles, and the second is it's not a matter of simply teaching someone to "drive" equipment. They have to be able to not only understand all manner of technical and physical things, but be able to react to unexpected situations in a clear headed fashion.