
sometimes its the click of the lead releasing that puts them in the mode of deaf ears!! a trick is to wrap the lead around the collar and tuck it in .
I would go right back to basic training on an extended lead ie: puppy recall (running backwards calling him to you then in a sit and treat)
They get bored... I have a girl who was in a team and occasionally she would get deaf ears ..or walk quiety and slowly away in the middle of a team training class like she was sneaking out of class.. when everyone was in a basic sit stay (which was actually very funny but we didnt let her see us laugh) it was her way of saying I am bored lets do something more interesting such as agility!! <BG> I trained 4 times a week at that time which was too much of the same thing so I had a break did stuff at home returned to the puppy close work and she loved it.
I agree do your recall around the house too not just at class even if they are in thier bed or wandering around the garden always have a nice smelly treat handy then 'go play' .
I now use a ball ..all my dogs are ball obsessed I take a few to the park they also each carry one (thier choice) I keep the rest in my pocket ..they dont take thier eyes off my pocket just waiting for me to throw the balls.
Must admit I am usually with someone and we play football with the dogs which they love so they never wander or have any interest in other dogs in the park .
good luck