This Fender Knot was spotted recently at a Puget Sound Marina. They are loosing massive style points here and while the knot will hold, I suspect that it might be difficult to untie. See below for some options to restore the style points and make line handling easier and safer.
A better solution might be to to use a Spar Hitch. The Spar Hitch is similar to a Clove Hitch except the bitter end is tucked under the line going to the load, this means that the heavier the load the tighter the knot gets. The load can pull at different angles.
Another quick easy and secure knot to tie a fender is Lee’s Fender Knot. This is also a great knot for hanging coiled line.
Both of the above knots are quick and easy to tie and hold well around small diameter slick surfaces.
Round Turn and Two Half Hitches, great knot for tying fenders and all around useful knot
The old standby, a Round Turn and Two Half Hitches works very well and is the knot that I use the most.
A well tied Cleat, very high style points
Remember that part of boating is style as well as safety and one of the first things visitors to your dock and boat see is how your cleats and fenders are tied. (See also How to Tie a Cleat)
Toe Rail Fender Knot
The Toe Rail Fender Knot is a great way to tie fenders if you have a toe rail on your boat that is perforated. This lets a fender be tied almost anyplace along the side of the boat without hanging the fenders from a lifeline (lifelines are not as strong).
Thanks for your interest in and support of boating Safety.
– c/m –
Boating Safety Tips, Tricks & Thoughts from Captnmike 
While the first knot you showed in this post does remind me of a frustratingly tangled necklace, I can’t help but feel like the other three knots you pictured would get loose far more easily. I think that it’s probably because of the fact that there’s a strand that’s just kind of sticking out in each one. It reminds me of a shoelace that is about to become untied. Then again, I don’t know much of anything about boating, haha. Have you used either of the knots you suggested and found good results with them? Just curious.
I have used all the knots shown and they all work fine. The Spar Hitch looks so simple but half inch line will hold on 1/4 inch dia. polished chrome rods. Not many knots will do that. I know several skippers that have changed over to the Spar Hitch because they were loosing fenders and now no lost fenders.
Another factor in knots is that you need to be able to untie them quickly when used for things like a fender. Some knots will jam under load and while that keeps them from coming undone. cutting the knot off or needing to pick it apart with a marlinspike can be a problem.