How about a ball pit like at Chuck-E-Cheeze or having rollers (like on a conveyor) made out of PVC pipe? This wouldn't cover the whole field but instead form a "hazard area" that you could either try avoiding or designing a robot to deal with it. This would partially divide the field and your score could be partially based on how long it takes you to get across the field. You would either take the "scenic route" and avoide these but lose points or if your robot is capable ignore the hazards and go staight across.
Or I still like the snow idea. Nothing like seeing a robot on skis or a snowboard
For the southern and southwest teams don't worry, we have plenty of snow up here and we'd be happy to ship you as much as you want.
I might even try to convince those in New Hampshire to include snow in the KOP for you too!
