When installing panels into an window opening or frame, you often need to secure it while you finish puttying or use other forms of weather proofing.
If you use sprigs (headless nails) or even carpet tacks, use them where there are leads meeting the perimeter. There us less chance of a stray hammer strike hitting the glass. It is more likely to strike the lead and so cushion the impact to the panel. I also use a straight putty knife behind the nail or sprig to avoid even the chance of a strike directly on the lead.
These precautions, with suitable modifications, are applicable to copper foiled and fused panels.