Today I saw a small hole while mowing (maybe 6 inches wide). I decided to mow over it and straddled it with my mowers tires (60 inch Toro ZTR).Next thing I know I was looking up at the shy. The ground had given way and my mower was hanging by its ROPS and deck with about two more feet to the bottom. Once we wenched it out we saw that a 2 inch sprinkler main had burst and created a sink hole. I feel lucky that it could have been worse but one more thing to worry about.