Local sheet metal co's here seem to keep them in stock from galvanized to copper in several diameters. Very simple...Round pieces of metal that slip on the stack like a sock & they have mesh screen on top. Would you go with Stainless or aluminum?
Doesn't have to be a metal, I'm open to alternatives as long as it does the job & doesn't interfere with the stack doing it's job AND MUST keep critters out. What about something like these?