That's a good point on the visibility of stuck heads.
As far as the heads getting pushed down; We do lawn maintenance and use everything from 21" push mowers to 60" 1500 pound Z's. Usually areas where you use large heavy mowers the sprays aren't that common. However, the footprint of the drive tire on most big machines is 12 inches wide and they aren't inflated with much pressure, so driving over any sort of head - rotor or spray - has never caused a problem for us. The only time we've had an issue with this is if the ground is completely saturated and we're making ruts. Usually don't mow in those conditions anyway though.