Toilet training rabbits?

My rabbit always went to the toilet in her hutch instead of her grazing run which is lined with wire mesh because she always try's to burrow. I now have another rabbit who shares a hutch(a big hutch by the way) with my first rabbit. My new rabbit has started doing her buissness in the graizing run which is connected to the hutch. The run is such a night mare to clean out because of the mesh but I cant remove it because one of them burrows and now my first rabbit is also doing her buissness in the run. I have tried loads of brands of cat litter (that is also for rabbits) and a litter corner for rabbits but they lie in it instead and dont use it. What else can I do? I dont want to remove the mesh and seperate them and they like to graze. What should I do? The run is practically impossible to clean out.