Mike, if your sump pump is above the water line of your pond you should not have any problems at all with the water coming back in. Now if the line is not buried below the frost line(as deep as 6" depending upon your ground make up (clay, sand, etc.) then that would explain why it blew the check valves. Obviously as water freezes it expands thus causing a real mess.
Back to the sump pump, most people's pipes are at or near the surface of the pond as far as the outfall of the water. As far as the sump pump shutting off, they typically run for a 10-20 seconds at most depending on how much water they have to pump down. Then when the float reaches a certain height it will kick on again.
I hope this helps, if not hit me again and see if we can't figure this out.
BJ
