The solid gravel guards are very handy for use as rod tube straps - I put three or four metal rod tubes together and pull the gaitors over them and they are just perfect for carry on. In fact one of the tubes is a Loomis IMX with handle and I carry it with that while the other Sage tubes flank the middle tube.
For river wading a pair of socks over the waders (on the outside) between the feet and the boots are usually enough. This trick extends your wader life by years too. Of course a pair of gaitors over that is the ultimate.
In sand, surf, salt just the socks don't cut it - the ankle must be sealed off because of the fine suspended sand. The socks may still extend wader life but once you go to the extreme of color-coordinated duct tape
you don't get enough inside the boot for it to matter.
This all depends on whether you use a gussetted boot - if you are wearing a boot with vent holes or is unsealed fine sand will accumulate in the boots regardless. A good test is to fill the boot with water - if the water can get out then it's not a good boot for the surf.