Some knots are only useful under tension; absent that, they can get sloppy without too much effort. I'd say the clove hitch is one such example.

But it can be fixed in that regard by turning it into a constrictor knot instead, IIUC.

A “round turn and two half hitches” (ABOK #1720) is what I’ve been told is a better alternative for tying fenders to a boat that will be left unattended

if the clove hitch is tied near the end of the rope, you can take the tail and tie an overhand knot with it around the standing line to back it up

See my other comment on this post: https://news.ycombinator.com/item?id=37685921