The reason you guys are having trouble on grass with wheel pants is simple. You have no support on the outer side off the pant. Here's what I do:

1) Rough up the inside of the pant, and polyurethane 1/8 AIRCRAFT ply on the inside (postage stamp size). When that is cured, 3/4 fiberglass and epoxy resin the area slightly larger than the wood you inserted.

2) mount the pant

3) leave the axle long enough so when the pant is screwed on to the gear, it just touches the outer edge of the pant.

4) get another postage stamp size piece of 1/8 or thicker plywood. drill a hole through the center, the same size as your axle. Using the same method in step #1, attach this piece to the outer side of the pant, making sure the pant is mounted and centered

You now have complete support through the whole pant, giving it tremendous strength. I have models with pants that have over 150 flights on them, and the pants are as good as new, except for maybe some paint rubbing off. Our field is smooth grass, but i have eeven flown in rough pastures with no problems.