Actually one can follow the ex&le of pros and use a very protective device called a lens cap. Often these are supplied with lenses when purchased. If not they are available everywhere photo supplies are sold.
The method of operation is simple. When one is anticipating a photograph to be taken, the camera is removed from the working bag, and the lens cap is removed. Upon completion of the shoot, the lens cap is once again installed on the front of the lens and the camera is put back in the bag.
When multi-coated lenses were first announced a few decades back, a Nikon rep came by to demonstrate them. During the demo, he casually butted out a lit cigarette on the front element of a very fast and very expensive lens. He spit on the lens and wiped off the residue with a rag he pulled from his pocket. These surfaces are remarkably tough.
A lens is as sharp as its weakest element. Why add two glass surfaces to the optical path when you already have a lens cap? Filters are for changing the colour balance or adding effects to your picture and the trade-off is worthwhile. If I were doing industrial shots of sand-blasting or anything else involving high-velocity abrasive particles, certainly it would be worth the trade-off in that case. If you are photographing a sandstorm in the Sahara, velocities are low enough and the particles not abrasive enough to be worried.
If you are using the filter to protect against an unexpected blow you might receive to the lens when photographing, if it is powerful enough to warrant protecting the lens, the emergency technicians will be extracting camera bits from your head on the way to the emergency room or morgue. At that point, a scratch on the lens is the least of your worries.
larry!
ICQ 76620504