Just an idea, but maybe take him ratting. My Dogs go wild over rodents. My Dogs spend hours looking for Mice in my Garden. I have a Walnut tree. fruit trees and a lot of Berry bushes to draw Rodents. I have no doubt if mine learned Rats lived in trees, they'd be looking in every tree around. Show them a Rat and they go nuts. Once he gets hot on Ratting, it should be easy to get him really interested in tree Rats. Just an idea.