Simms flats boots, I bought a set and have used on 5 different trips. With the previously mentioned cheap athletic socks/neoprenes (Simms variety) and high top/ankle supporting boots never had an issue.. I've found quicksand holes on a Cuban flat that looked like a parking lot, and went right to my thigh in 1 step, or soft sand/uneven bottom, without a rolled ankle. Also used on CXI bommies for GT's that was covered in staghorn coral (and which didn't even faze the barefooted guides, which was something to see) to the sharp bottom we found in Hawaii. They're solid and worth every penny IMO. And never had an issue with sand.