I have a stray dog that I want to do some clicker training with and he screams and tries to hide when he hears the click. Do you have any suggestions for a quieter clicker?

I take in and rehab strays. I do a lot of trick training using clickers. However, I have a Blue Heeler who screams and tries to push himself under the bed or cram himself into the corner of a closet when he hears the click. Someone suggested using a retractable pen, but the timing with it is unreliable. The Heeler was not scared of its sound, though, so I am hoping a quieter clicker would do. I saw two in the Leerburg catalog that advertised as being having softer clicks. They were the i-Click and the Clik Stik. All things being equal, I would prefer the i-Click, but if the other is significantly softer, I would get it. Or do y'all know of something else that could be used as a marker that would have the same accuracy as a clicker? I know you don't use clickers a lot, but they work real well for teaching tricks to these abandoned dogs. They really enjoy the trick training--they loosen up and get a little confidence.