hardside luggage sans zippers would prevent the ole zipper exploit, but aren't you overlooking the fact that you'd need a lock to secure a hardcase and it's fairly easy to snip them? moreover, do you really think the inability to reseal a zipper [if you buy that zipper lock] is really going to deter a thief? personally, i don't think so. and using such an uncommon thingamajig would only draw more attention to your luggage.

i use a plastic ziptie on my luggage to deter the casual rummaging and to offer a visual aid that my luggage has been opened. i try to only pack inexpensive/easy-to-replace clothes/shoes in my checked luggage. anything expensive or favored clothes go into my carry-on.