In reply to probablylost:
I'm afraid I can only give you the classic UKC answer of telling you what I have. I'm not really sure what you mean by O-ring, I don't think I have any on mine.
I have a pair of Alpkit gaiters and they seem to do the job. They've got a bit of cord that goes under the shoe, a hook on the front, and elastic at the back. I've used them a lot and never had a problem with them not staying on. They're also cheap, tough, and don't seem to absorb much water. My only gripe is the top closure seems too big, and I don't think I've got particularly skinny ankles. Never an issue in practise though and at some point I'll move the velcro.