That's a really bad series of hits. Sounds like you've tried everything possible to make the toad more visible except putting road flares on it.
It is amazing how many people drive without engaging their brain. A coworker was front-ended while sitting at a stop light when the driver ahead suddenly shifted into reverse to back up from the intersection. He told him that he did not see him. Obviously he never even looked in his mirror because my friend had a fluorescent orange kayak strapped on his roof.