Thanks to all for your comments.

Hoping to never encounter a rock garden, I think I will just add a second layer of 4 oz. cloth to the bottom. As one poster mentioned, if it gets chewed up badly enough, it is no big problem sanding down to the glass and applying another layer. I've used 4 oz. glass and 4mm okoume throughout and have been very careful about squeegeeing out excess epoxy, so the boat is coming in at under 45 lbs. and I would like to keep it that way.

Thanks again,

Chris Luneski