SIMMS makes their Intruder boots with integrated gravel guards. Per pair they're like 2.6lbs. I bought them intending to use them only for hike-in trips but I use them all the time. These are now my go-to wet wading boot. Oversized, they'd go over waders fine. Their Freestone is also light. Super-light are the Riprap Shoe, but they're like low-cut tennis shoes and so don't offer any ankle support.
Owner, Yellowstone Country Fly Fishing
Head Guide, Parks' Fly Shop
Fly Designer, Montana Fly Company
Author, Yellowstone Country Flies and River Characters