Hehe, the difficulty actually does reset. The bug is a bit more sinister than that; a new spawn timer is initiated every reset, *without* removing the old one! So you get 2x the rocks the second time around, 3x, 4x, etc.
Ooh, tricky! Well, I had a bit of fun anyhow; I got to about 290...
I've tried building something like this in the past. It's really tough! Good work!
