Sally; thanks for your input.
I just finished my mod today. 8)
Purchased a brass-finished "corner iron". Very thick - very strong. The pre-drilled holes are the same size as that on the plastic tab. Hacked it off about 1/4" longer than the original tab, beveled the edges facing the door and - Viola (as my Mrs. Malprop friend would say), all fixed. Works fine.
For extra tamperproofing, I might reattach the white tab immediately next to it, on the hinge side of the new tab, so that it can't be forced sideways from the outside (thus releasing the upper door) with a knife or screwdriver blade.
I'm not paranoid, even if everyone is out to get me!
Denny_A