Paul, thicker layers of epoxy thickened with troll powder (or whatever) isn't going to work as effectively as a tougher material like a chunk of UHMWPE, more glass feathered in, layers of tough sythetic cloth, a recess cord or rope, half oval of brass,etc.
I've built up a l/8" thick feathered layer of 4oz s-glass glass that's pretty tough out of about 6 progressively smaller bias cut strips, two layers of Dynel work but make SURE to squish it down with saranwrap(it'll be pretty prominant), half oval brass isn't easy to curve around corners (still figuring best method of attachment)but it looks good, the last solution I'm going to try is recessing a cord of "dynel" (that's what JRSweet calls it) into the bow and stern then glassing over it.
Then again 4 thin layers of bias cut 6oz e-glass is pretty cheap and lasts awhile.
Oh forgot, I met a fellow that used split hydraulic hose glued on with polysulfide adhesive. I expoxied on some strips of polypropelene tiedown webbing on a Pirough because the bozos that borrowed it were too drunk to carry it.