Stop drilling is how aircraft mechanics deal with small cracks in sheet metal skins, as well as acrylic windows, etc. I assume the same would work for fiberglass. Sharp corners create stress risers which can lead to cracks.
Thread drift, sorry -
The deHavilland Comet suffered multiple catastrophic failures due to stress risers that occurred with sharp corners. The phenomenon was not well understood at the time (1950's) but the engineers quickly figured out the cause and aircraft design, especially for pressurized aircraft, changed as a result.