I keep an eye out for brightly colored zip ties. Hot pink and orange are my favorites. No, they don't protect the contents by themselves, we also use combinations locks, but when we claim our luggage it's easy to tell at a glance if someone has been into or attempted to get into our luggage and we can inspect it right there. Chances of airport personnel having wild colored ties to match ours is very slim.
The really valuable stuff is in our carry ons but the outside pockets still might hold some interesting stuff!
Luvdiving....We've always carried nail clippers for the zip-ties so if those are ourlawed, I don't know what we'll use. If nail clippers aren't allowed, I doubt a small Leatherman with pliers will be either.