Some people on this site use snoods to keep their dogs' ears crud-free. Search the site for "snood". Another thing you might consider, and this is just a guess on my part, is applying a silicon-based spray on the ends of the ears. Something like Show Sheen for horses. It might keep the stuff from sticking to his ears, and since it's made for horses, which have sensitive skin, it shouldn't irritate a dog's ears.