'Clicker Training for Your Horse' by Alex Kurland is good too. I'm planning to start Mayoral again with this in the New Year. I tried last year but managed to lose 3 clickers in as many weeks, and I have to get them sent from UK. I have discovered that some jar lids that have the pop up 'safety button' work pretty well too, they're just not very loud. Keep us posted, I'd be interested to know how you get on.