Outdoor run: what to put over mud?

Does anyone have any suggestions for what to put over the earth of a now-muddy outdoor run? We use rubber chips for the hens, but rabbits would probably chew those. I'm wondering about the tough rubber mats used for horses' stables, but maybe the rabbits would have a chew on those too? Has anyone tried woodchip - if so, any safe-for-rabbit suggestions? Thank you.

I have used stall mats, and some rabbits do chew on them. My rabbits never ate the rubber. If there are any low spots on the mat, water will pool in that spot. Stall mats tend to turn the rabbits' fur on their feet black. Wood chips can get moldy from getting wet. I don't know if there is an easy solution. I think the best solution is if you could put in a drain, like the ones used to keep patios dry, but that might take some landscaping.

I use carpet grass for my run. it's on top of a wooden platform so I don't know how it would hold up over mud tho.

Thank you both.