I would say fiberglass and wood boats are fairly durable.  I have scraped my boat across some rocks when heavily loaded and it does scratch, but mainly the varnish.  I have made a few deeper scratches into the fiberglass, but none through it.  My advice is that knowing the conditions you will be subjecting your boat to, put an extra layer of glass on the bottom and a couple of extra rub strips on the bow and stern.  

James,

Here's what happpened when my overloaded pirogue scraped over a rock in the Potomac River up in the hills nears Hancock, MD. The current was 6 mph, the boat is 1/4" okoume covered on the bottom with 4 oz woven glass.The rock never made through to the wood and the trip continued. When we got home, a little sanding and epoxy made everything as good as new.

Because of your meaner environment, in addition to what Casey reccomends, I definitely recommend completely glassing the inside, not just the cockpit area. When a rock tries to punch through a hull, there's a lot of tensile stress on the inside surface. The best way to fight it is with a layer of glass on the inside.You can do the entire boat, or just the hull and the sides to keep the weight down. If you skip filling the weave on the interior glass, that also helps keep the weight down.

If you're still nervous, you can go to the next level and fill all the non-cockpit spaces with 2-part structural expanding foam. It only weighs 2 lbs per cubic ft and will make your boat pretty much unsinkable. This is the Coast Guard approved stuff, not the insulation you find at Home Despot. Think of it as the ultimate endpour. You'll be able to tap dance on the deck.

Have fun,

Laszlo

Keep in mind, since you built it, nothing is "irreperable"... just a question of how much damage needs to be sanded or cut away before the repair begins... besides that is all part of the adventure.

Laszlo,

Was "Despot" just a typo?

It depends a bit at how sheepish you will be to use it once you spend 100 hours plus building it and making it beautiful.  I know in my case (live in Michigan) we are generally on small lakes and rivers and I can pretty much keep away from danger.  Still, I hate hitting stuff and scrathing it up.

 If you conditions out there are going to keep you from going where you want to go and getting on the water than I'd paddle whatever you want that gets you paddling.  I personally could handle the thought of running up on rocks with any frequency.  Worked too hard on them!

I will say however, nothing is better than a wood boat and I love paddling them.

Sorry - I meant "couldn't" handle running it up on rocks. 

THanks again for all the replies =)

 Klaver, 

 I've raced bikes I built and put hard parts on the ground before, I'm not going to avoid using it, and I'm not afraid of scratches. I don't dye my hair, as I've earned all my greys, and I'm ok with my kayak earning it's marks too (not that I won't repair it and keep it in proper order) my main concen is if I'm going to try to beach it on the islands and be left with a nice pile of firewood and no way to get home. It sounds like that's not the case. :) 

-- James