At the recent auction of equipment one of the lenses had a damaged front element. A repair was going to be at least £300. Damaging the front element is very easy to do but easy to prevent.
Buy a filter!
Some folk answer that sticking another piece of glass in the way degrades the image. Well it might but nowhere near as much as a scratch! However having done some experiments I've never been able to see a noticeable degradation but then I buy good filters. These are multicoated in order to reduce reflection.
I buy B&W UV filters from Robert White.
When Nora got a new camera the camera shop only had a cheap filter, so I bought one from RW as soon as we could. As I was doing the swap I inadvertently did an experiment, as you can see below.
Guess which is the cheap filter and which is the B&W filter.
The B&W was about double the cost of the cheap one, worth it!