I've got a pair of gaiters which I've hardly worn. On the few occasions I have I've noticed that they seem to lack "body". No matter how I secure the tops below my knees, after about half an hour or so of walking they've collapsed around my ankles. I've thought about "stiffening" them with a solution of PVA glue.
I stopped wearing gaiters years ago; I just use stop tous/ankle high gaiters to stop snow and stones falling into the top of my boots. Those and overtrousers work fine for me.