You've probably got a couple of things going on. Under-kneading and poor loaf formation technique.
You're not getting enough "surface tension" on the dough for it to hold its shape. The easiest way to solve it is to use the pull down technique until you have a real tight skin, before going on to actual shaping; then, shaping in such a way as to keep the skin tight and outside; all the while, careful not to lose too much lift. It's not that difficult once you've practiced enough to develop some touch. It might help to read this
Kneading precedes formation. Different "artisanal" breads have different levels of hydration. That they ALL feel slack to you screams under-kneading. Whatever kneading technique you use, you're just going to have to keep kneading until the dough is smooth and no longer sticky. Except with the slackest doughs, that usually happens at about the same time the dough passes the window pane test -- for the same reasons.
Edited by boar_d_laze - 3/28/10 at 11:06am
You simply have to be sure the dough passes both tests before going on to the first rise.
You can also do something towards stiffening up the feel (and behavior!) the dough (without actually making it stiffer) by doing an autolysis with a few "French folds" in it.
The whole autolysis plus French fold thing is fairly new to artisanal baking, but seems to be one of those few, new things destined to become "traditional." I now do it with nearly all of my breads.