Install a hardened glass in front of chimney
There is standard hardware for the job, from things like glass inserts in stair/deck railings and glass signage.

Try "glass standoff bolt" in a search engine. You'd put an anchor and stud (or screw, depending on the standoff design) into the masonry and attach that hardware to/with the stud/screw. Looks decent, easy to unscrew when needed.