you can use a special word as a marker instead of a clicker (i had a dog who was afraid of the clicker as well). i use "yes". you could also try an i-click, which has a softer click. that might be less scary. you could also try clicking a retractable ballpoint pen.

i don't have any clicker training books, but check out clickertraining.com for tons of really excellent (and free) information on clicker training.

Thanks Katie!

Try wrapping the bottom of the clicker in electical tape. It muffles the sound of a clicker. Also another alternative would be to use a pen that has a top that clicks when you push it. It isn't as loud. Also try clicking with your tongue. Using a word doesn't mark the behavior as well for me. Afterall, an animal hears your voice daily. It is harder for them to distinguish what they did right & it is hard for you to spit it out at the right time! Karen Pryor has some great videos at clickertraining.com!