The lockkeeper at Chersey Lock showed me a knot to use when fixing the fender to the handrail. It was great because you only had to tie it once, then just move it up and down depending when the fender was required. But i can't remember what it was called or how to do it.
its different from any other knot i've seen. He tied some sort of knot around the long bit that the fender dangles from and you could slide this knot up and down, thus moving the fender.
Start off like a clove hitch , but continue to roll the working part over the line (trapping it) finish with a hitch you can slide the knot one way but not the other hope this explains it .