My bikes see lots of use, mostly as commuters. They spend time outside subjected to elements which I cannot control. Often times I’ll leave my bike parked at a bike rack and return hours later thinking “strange, i could have sworn that my headlight lens wasn’t cracked” . The same goes for unsightly fender dents. I have no idea how they happen, but for me they are one of those things which make a bike look very used. Even more than scratches.
So a while ago I decided to repair some dents in my fenders. Stainless steel is hard and doesn’t dent easily, but when it does you’ll have a hard time pulling them out. If you have aluminum fenders you’ll probably be pulling dents more often, as the metal is softer, but because of this they are much easier to pull or “push” ;)
To push out dents the only tool required is something everyone should have at home, a teaspoon. Because the spoon is curved it makes a great tool to massage out the dent. It is best to remove the fender from the bike completely so you can apply good pressure from the opposite side. A rolling motion with heavy pressure should show good results. If your thumb starts to hurt, then take a break and go back at it later. Patience will be rewarded greatly!