There's a great site here http://www.equineclickertraining.com on equine clicker training (yes you can use it with your horse - it's great for teaching ground manners as well as teaching new commands under saddle).
Alternatively, if you're just after k9 clicker info, you might want to try...
A few people I know are using the 'fly visor' - it seems to sit well up off the eyes. It was in your horse a couple of months ago, if you google it there's a review on the national horse and pony network.
Hope this helps!?