I use the thin, small zip ties which are a beast to open without damaging. Through the zip pull(s) and round a D-ring or other bit of the bag so the zip can’t be popped out and back without leaving a few links showing.
I go on the principle that I can’t stop someone from getting into my bag, but I can jolly well see if it’s been tampered with, either by security or the bag chuckers.
Years ago I was flying with a lovely DeKerf in a soft bag, and someone trod on it hard enough to push the front wheel axle into the downtube, leaving a crease. I complained to the airline and was told I had to report damage at the airport. So from then on, I always unpacked any bike I was flying with to check for damage before leaving the terminal. Really, really annoying, because you either want to get to your holiday destination or get home, but I felt I had no choice.