"Mark" is a pretty hard word for me to say personally. I use "Yes!" with my pups, but I make sure the sound and pitch is very distinct. Get all your fervor and excitement and say "Yes!" enthusiastically (like "Yes! Oh my God I won the lottery! Yes!!").

Every time Nino perks his ears or looks at you when you say "Yes!", treat him. Do this periodically for at least a few days. Eventually, he learn that "Yes!" = treat. This is what "loading the clicker" is. If you don't load, the dog has to learn through trial and error what the clicker/marker means. And, as you Nino has shown us all, trial and error takes a long time to 'click' with the dog After that, it'll become a habit for the both of you and "Yes!" will come naturally.