In reply to the Yeti gaiter comments, here's my experience. I think they are brilliant
I am still using a pair bought in 1984, and have had new rubber rands fitted by LSR just once. They are difficult to put on but then they wouldn't be any good if they were easy. Just to be clear I'm talking about the standard current Yetis, there were another design some years back (Yeti Attak I think they were called) which were made of a lighter rubber and were relatively easy to remove or put on whilst wearing the boots, these could be identified by a ridge on the rubber that went around the front of the boot and toe, the ridge locating in a groove in the boot, basically designed to help the toe stay in place. I don't believe these are available now.
Back to the existing Yetis, where the rubber rand is very tough. mention has been made of super gluing the toe to the boot and this is something I've adopted, and never had a problem since, but then I only use the gaiters on my winter boots, basically they never come off, no need to, for winter. The gaiters being of such strong rubber means they are not effective on boots that flex such as summer boots, this being the main cause of the toe slipping up, they are designed for stiffer boots, mine being B2 winter boots.
Over the many years I've used them I have found them very impressive, not only can you cross streams without water ingress, but the original ones I have are also lined with Thinsulate, keeping the covered area cosy too. A word of warning on the ability to cross streams/burns, they are not watertight along the zip and the waterproofness is reliant on the Velcro that runs the length of the gaiter (and to some extent the zip), as someone else posted if you are in water up to the depth of the boot you'll be fine, once over the boot height and up over the gaiter, don't hang about
that said, far better than no gaiter at all. It may be that the Velcro on mine being 34 years old now, is not quite as 'sticky' as it use to be, (when new I did wade across a stream on the Pennine Way up to the height of the gaiter with no ingress) but again, I try and avoid crossing streams/burns, and its certainly still good enough for snow. Again it could be replaced by LSR who did an excellent job replacing the rubber rands.
The normal gaiters that are available, I have long since binned, as I find them of little practical use, I don't like wearing them and legwear these days has scuff areas on the bottom saving wear on the trousers.
The one other benefit of Yetis, often overlooked, is the protection it affords the boot itself. Good winter Winter boots are not cheap and the gaiter covering the entire boot can give extra life to the boot. My winter boots, Berghaus Kibo's, are extremely comfortable, as comfortable as my summer boots in fact, so I'm hopeful they will last many more seasons