It is winter in Maine! I pulled on a job today, Snow on the ground with a slight incline and Parked the pump. Chatting away beside the drivers door. The pump slides down the hill about 10 Feet! I almost SH#! my pants! I put that one in my notes! 

wheel chocks brother. unless it went sideways. then you're screwed.

and often wheel chocks won't work on ice.....and remember not to set up your outrigger pads on ice on a incline....dig it down to bare ground....